Background: Secondary school students are exposed to risky sexual behaviors that put them at certain risk of negative consequences. The aim of this study was to investigate the sociodemographic factors as predictors of sexual behavior of secondary school students in Lagos State, Nigeria. Materials and Methods: A survey design was used for the study. The data were collected using self-developed structured questionnaire called youth sexual behavior questionnaire, the co-variates collected in the questionnaire were: Gender, age and sociological factors. The instrument had test-retest reliability co-efficient of 0.78 while purposive sampling technique was used to select the schools and respondents. Totally, 2720 students were randomly selected for the study and inferential statistics of multiple regression, mean, t-test and ANOVA were used to analyze the data. Results: Results indicated that all the three co-variates used in the study were significant. Which shows a significant value for gender, age and sociological factors respectively (t = 6.753, P < 0.05), F(3, 2350) (79.930, P < 0.05) and F(4, 2394) (260.020 P < 0.05). Majority of the students were of the opinion that they engaged in premarital sexual activities despite its attendant consequences. Conclusion: Gender, age and sociological factors could infl uence the sexual behavior of secondary school students in Lagos State significantly; it was also observed that most of these factors negatively infl uence youth’s sexual activities.