The study examined the effect of Behaviour Intervention on adolescents’ sexual risk-behaviour. 120 adolescents comprising ( males 56, mean age = 19 years ) and (females 64, mean age= 18.6 years) were selected purposely from a population of 1168 SS11 students in the eight public schools in Awka urban using a survey study . The participants that had high mean score of sexual risk – behaviour, in the survey study, from a sexual risk-behaviour test (males’ mean score =47, females’ mean score = 42) were selected for intervention training. The test has a validity of .94 and a reliability of .82. The subjects were randomly assigned into the three treatment groups, namely: Assertive group, self control group and control group, with 40 adolescents in each group. A random group design with three independent variables and a Multivariate analysis of variance (MANOVA) were used for the study. The result of the data analysis showed that participants’ scores on the test for those that participated in intervention training in assertive and self-control groups differed significantly from those participants in the control group (P =.03).However, the Scheffe pair-wise comparison test indicates that those in assertive training group had greater change (P=.017).The study concludes that Behaviour Intervention (assertive training and self-control training) had significant effect on adolescents’ sexual behaviour .