This study examines the correlation between peer influence and sexual behaviour of secondary school students using Ijebu-Ode Local Government Area of Ogun State as case study. A sample of 200 adolescents drawn from JSS 3 – SS 3 classes of four mixed public secondary schools was used. Three research hypotheses were formulated and tested using stepwise regression analysis. The findings show that there is correlation between peer group influence and permissive attitude toward sexual practices among secondary schools students. There was no difference in terms of age and sex. Boys tend to be more sexual active than girls, while involvement in sexual activity increased with age. The study established that peers exert great influence on the adolescent through various means. These include exposure to pornographic films, pornographic magazines, romantic novels, and discussion of sexual issues. The study also discusses the dangers of this situation for the adolescents. The study recommends that relevant sexuality and reproductive health information should be provided to adolescents through joint effort by parents, counselors and educators so as to enlighten them on the dangers of pre-marital sex.