AbstractBackground: Peer counsellor programs are one of many countermeasures for current issues in adolescent mental health. Peer counsellors need to have adequate capability and self-efficacy especially in basic counselling skills to be able to help their peers in their daily life. A validated training module for peer counsellors in mental health context has not yet been developed in Indonesia.Aim: This research aims to develop, and evaluate content and empirical validity of a training module for adolescent peer counsellors in Indonesia.Method: A training module was developed based on a systematic literature review. Expert judgment was elicited to ensure content validity, while a quasi-experiment with two groups control design with a pretest and post-test measure was conducted to evaluate empirical validity. Thirty experimental group subjects and 14 control group subjects were involved in this study.Results: Expert judgment showed the training module had satisfactory content validity, fulfilling statistical consensus requirements. Analysis using EffectLiteR showed that peer counsellor training had a significant effect on self-efficacy with a significance score of 0.019 (p < 0.05) for average effect.Conclusion: The module has adequate content and empirical validity to increase counselling self-efficacy in adolescent peer counsellors.