Aggressive behaviour is a serious malady to students, especially those in their adolescent stage. This study investigated the effect of Socio-cognitive skills training on aggressive secondary school adolescents in Anambra State, Nigeria. One research question guided the study and two null hypotheses tested at 0.05 level of significance. The design for the study is quasi-experimental, non-randomised pre-test and post-test, control group design. The population of the study was 323 senior secondary school adolescents with high aggressive behaviour in Anambra State. A sample size of 32 adolescents were purposively drawn from two schools with the highest number of adolescents with high aggressive behaviour and used for the study. Instrument for data collection was adopted from Buss-Perry Aggression Questionnaire (BPAQ). The internal consistency reliability coefficient for Nigeria sample is 0.80. The completed instruments were scored following the scoring instructions provided in the BPAQ manual. Mean scores were used to answer the research question, while the null hypotheses were tested using Analysis of Co-variance (ANCOVA). The norm of 70.25 provided in BPAQ guided the decision. The finding of the study revealed that socio-cognitive skills’ training was effective in reducing aggressive behaviour of secondary school adolescents. The findings further revealed that the difference in the effect of socio-cognitive skills training on aggressive secondary school adolescents was significant when compared with those in the control group. Based on the findings it was recommended that the practicing counsellors and therapists should adopt the use of the technique in managing aggressive behaviours of secondary school adolescents.
 Keywords: Aggressive Behaviour, Secondary School Adolescents, Socio-cognitive Skills,Training