Section 120 — Evidence to impeach a witness
Statutory text (Thai original)
ถ้าคู่ความฝ่ายใดอ้างว่าคำเบิกความของพยานคนใดที่คู่ความอีกฝ่ายหนึ่งอ้าง หรือที่ศาลเรียกมาไม่ควรเชื่อฟัง โดยเหตุผลซึ่งศาลเห็นว่ามีมูล ศาลอาจยอมให้คู่ความฝ่ายนั้นนำพยานหลักฐานมาสืบสนับสนุนข้ออ้างของตนได้แล้วแต่จะเห็นควร
English translation
If a party claims that the testimony of a witness cited by the other party, or called by the court, should not be believed, on grounds that the court considers to have merit, the court may allow that party to adduce evidence in support of its claim, as it sees fit.
This English translation is provided for reference only and has not yet been firm-verified — always rely on the Thai original.
Firm annotation
Section 120 provides a controlled route for impeaching a witness's credibility. A party who contends that an opponent's witness, or a witness the court itself called, is not worthy of belief may, if the court finds the grounds have merit, be allowed to lead evidence attacking that credibility. The power is discretionary and gated by the court's assessment of merit, which keeps the trial from being diverted by baseless attacks. It complements the examination rules in Sections 116 to 119 by allowing rebuttal that goes to the weight of testimony rather than the issues themselves. In criminal proceedings it is applied together with Section 228 of the Criminal Procedure Code and Section 15 of that Code.
Why this matters in practice
If a key witness for the other side is not credible, this section is how you put that on the record: identify concrete, meritorious grounds and ask the court's leave to lead rebuttal evidence, rather than merely asserting the witness is lying. Because the court has discretion to refuse, the grounds you present need to be specific and supported. How courts weigh witness credibility is a recurring theme in the Supreme Court decisions collected on this site, and understanding that pattern helps you frame a persuasive challenge.
Supreme Court decisions interpreting this section
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Supreme Court Judgment No. 5172/2566 (2023)
Section 120 allows a party who claims that a witness cited by the other side should not be believed, on grounds the court finds meritorious, to adduce evidence supporting that claim, and in a criminal case this operates together with the court's power to take additional evidence under Section 228 of the Criminal Procedure Code.
The Supreme Court set out that, under Section 120 read with Sections 228 and 15 of the Criminal Procedure Code, where a party claims an opposing witness's testimony should not be believed on grounds the court finds meritorious, the court may allow that party to adduce supporting evidence, and it applied this to the defence's rebuttal of the injured parties' accounts.
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Supreme Court Judgment No. 8379/2557 (2014)
Evidence adduced under Section 120 to support a claim that an opposing witness should not be believed is not part of the acts alleged as the offence, and so is not subject to the ordinary pleading and witness-listing requirements that apply to evidence proving the case itself.
The Supreme Court held that rebuttal evidence allowed under Section 120, read with Sections 228 and 15 of the Criminal Procedure Code, to support a claim that an opposing witness should not be believed, is not among the acts alleged as the offence nor evidence a party must ordinarily list, so it fell outside the usual pleading and listing rules.
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Supreme Court Judgment No. 2731/2556 (2013)
Whether to allow a party to adduce impeachment evidence under Section 120 rests in the court's discretion, so a trial court that declined to admit a document the opposing party had had no chance to test did not act unlawfully.
Because a document had been introduced without the opposing party having had an opportunity to challenge its authenticity, contrary to Sections 88 and 90, the Supreme Court held that under Section 120 the trial court had discretion whether to permit the evidence, and its refusal to admit the document was not unlawful.
Curated decisions with case numbers verified against the Supreme Court database. English renderings are the firm's editorial translation for study.
Frequently asked questions
Can you present evidence that the other side's witness is lying?
Under Section 120 you may, if the court finds your grounds have merit, be permitted to adduce evidence that the other party's witness should not be believed. Allowing it is at the court's discretion.
Does the court have to allow impeachment evidence?
No. Section 120 makes it discretionary: the court may allow the evidence only where it considers the grounds for doubting the witness to have merit, which keeps out baseless attacks.