In civil litigation, many people assume that witness testimony is the most important evidence presented in court. In reality, however, documentary evidence often carries greater weight.

Contracts, invoices, bank records, emails, text messages, official certificates, demand letters, and corporate documents frequently determine the outcome of a civil dispute. Because documentary evidence plays such a critical role, Thai law requires parties to disclose the documents they intend to rely upon before the witness hearing begins.

This obligation is set out in Section 90 of the Thai Civil Procedure Code, a procedural rule designed to ensure fairness, transparency, and efficiency in civil proceedings.

Understanding this provision is essential not only for lawyers but also for businesses and individuals involved in litigation in Thailand.

Why Does Thai Law Require Advance Disclosure of Documents?

Imagine arriving at court only to discover that the opposing party has produced an important document that you have never seen before.

Without prior notice, you would have little opportunity to determine:

• Whether the document is authentic.
• Whether it has been altered or taken out of context.
• Whether there are other documents contradicting it.
• How to question witnesses about its contents.

Allowing parties to surprise one another with previously undisclosed evidence would undermine the fairness of the judicial process.

For this reason, Section 90 is based on a simple but fundamental principle:

Each party should have a fair opportunity to examine and respond to the documentary evidence that will be presented at trial.

Advance disclosure helps ensure that both sides can prepare their cases properly, reduces unnecessary disputes during trial, and enables the court to determine the facts more efficiently.

Ultimately, the purpose of Section 90 is to promote a fair trial rather than create procedural obstacles.

What Documents Must Be Disclosed?

As a general rule, any party intending to rely on documentary evidence at trial must provide:

• One copy to the court; and
• One copy to the opposing party.

The documents must ordinarily be delivered at least seven days before the scheduled witness hearing.

An important practical point is that the statutory period is generally calculated from the date the documents are received, not merely the date they are sent.

Accordingly, parties should allow sufficient time for delivery, particularly when documents are sent by post.

How Can Documents Be Delivered?

Modern litigation no longer requires every document to be delivered exclusively through traditional mail.

Depending on the circumstances, documents may be served through various methods, including:

• Registered postal service.
• Courier delivery.
• Email.
• Electronic court filing systems.
• Messaging applications such as Line, where permitted by the court or agreed upon by the parties.

Regardless of the method used, it is essential to retain evidence proving that the documents were successfully delivered within the required time.

Proof of service may become important if a dispute later arises regarding compliance with Section 90.

What If Additional Evidence Is Discovered Later?

In practice, important documents are sometimes discovered after the initial witness list has already been filed.

Where the court permits the filing of an additional witness list, any supporting documentary evidence should generally be disclosed to both the court and the opposing party as soon as possible.

Failing to disclose newly introduced documents promptly may lead to objections from the opposing party and could affect whether the court accepts or relies upon the evidence.

Early disclosure remains the safest and most effective approach whenever additional evidence becomes available.

Are There Any Exceptions?

Although advance disclosure is the general rule, Section 90 recognizes several practical exceptions.

Documents Already Filed with the Pleadings

Documents attached to the statement of claim or statement of defence ordinarily do not need to be served again because the opposing party has already received them.

Documents Already in the Opposing Party’s Possession

If the opposing party already possesses the document or originally created it, additional disclosure is generally unnecessary.

Public Documents

Certain official documents, such as company registration records or certificates issued by government authorities, are publicly available and can usually be obtained independently.

Because these documents are readily accessible, separate advance disclosure may not always be required.

Documents Held by Third Parties

Where relevant documents are in the possession of the opposing party or a third party, the appropriate procedure is generally to request the court to issue a subpoena requiring production of those documents.

Extremely Large Collections of Documents

Commercial litigation may involve thousands of pages of accounting records or business documents.

If copying every document would impose an unreasonable burden, a party may request appropriate directions or relief from the court.

Documents Used Solely for Cross-Examination

Documents intended only to challenge the credibility of a witness during cross-examination are generally treated differently.

Requiring advance disclosure of such materials could undermine the effectiveness of cross-examination by revealing litigation strategy in advance.

Physical Evidence

Photographs, video recordings, maps, or physical objects are not always classified as “documentary evidence” for the purposes of Section 90, although different procedural rules may still apply depending on the nature of the evidence.

What Happens If Documents Are Not Disclosed?

A common misconception is that the court will automatically reject any document that has not been disclosed in advance.

In reality, the law gives the court discretion.

Depending on the circumstances, the court may:

• refuse to admit the document;
• admit the document but give it little or no evidential weight; or
• allow the document where fairness requires.

The court will often consider factors such as:

• whether the opposing party objects;
• whether the late disclosure causes procedural prejudice;
• the importance of the document to determining the truth; and
• whether admitting the evidence would serve the interests of justice.

Consequently, failing to comply with Section 90 creates significant litigation risks even if the document is ultimately admitted.

Practical Tips for Lawyers and Litigants

Proper document management is one of the most effective ways to avoid unnecessary procedural disputes.

As a practical matter, lawyers should:

• disclose documents as early as possible whenever feasible;
• allow extra time when serving documents by post;
• retain proof of delivery for every document served;
• promptly object if the opposing party introduces undisclosed documentary evidence; and
• rely on statutory exceptions carefully and only where genuinely applicable.

Although the law recognizes several exceptions, voluntary disclosure often promotes a smoother and more efficient trial.

Conclusion

Section 90 of the Thai Civil Procedure Code is much more than a procedural formality.

It reflects one of the fundamental principles of modern civil litigation: each party should know the evidence they must meet before the trial begins.

Advance disclosure promotes fairness, reduces unnecessary surprises, and enables the court to determine disputes based on a complete and transparent evidentiary record.

While the law provides several exceptions, timely disclosure of documentary evidence remains the safest and most effective litigation strategy.

Successful litigation begins long before witnesses enter the courtroom. Proper preparation, strategic document management, and full compliance with procedural rules often play a decisive role in the outcome of a case.

Siam Center Law Group Co., Ltd.

At Siam Center Law Group, we represent individuals, businesses, and international clients in civil, commercial, and complex litigation throughout Thailand. Our experienced litigation team provides strategic advice on documentary evidence, witness preparation, procedural compliance, and trial advocacy, helping clients present their strongest case while protecting their legal rights at every stage of the proceedings.