The aim of this study is to examine the effectiveness of cognitive behavioural group counselling on anger and aggression among male prisoners in Malaysian prisons. A total of 40 male prisoners were involved in this study. Subjects were assigned into treatment group (N=20) and control group (N=20) through purposive sampling method. Subjects were then divided into small groups (two treatment groups) and (two control groups) which each group consisting of 10 prisoners. The treatment groups attended eight sessions of group counselling process. State-Trait Anger Expression Inventory-2 (STAXI-2) and Aggression Questionnaire (AQ) were used as questionnaires to measure anger emotion and aggression behaviour. Data were analysed by using the analysis of covariance (ANCOVA) at 0.05 significant level. The results showed significant differences in the mean of pre-test and post-test on STAXI-2 scales such as state anger, trait anger and anger expression-out between the experimental group and control group. However, the results showed no significant differences for the scales of anger expression-in, anger control-out, and anger control-in between the groups. The results also showed significant differences in the mean of pre-test and post-test on aggression between the experimental group and control group. The implications of the findings and suggestions for future research are discussed.