The study examined marital sex and risky life style behaviours of in-school adolescents in Kwara State. The purposeof the study is to examine the factors that motivate risky sexual behaviours among in-school adolescent and alsotoexamine if gender, age, parental education level and school type will influence in-school adolescents intheirresponses. Descriptive survey was adopted for the study. Population comprised in-school adolescents in KwaraState. A sample of 250 respondents was selected through multistage method. Data was collected via researchers’ self – designed instrument titled ‘Risky Sexual Life -Style Behaviour Questionnaire (RSLBQ)’. Instrument wasvalidated by experts in test and measuremet and Split-half method was adopted to ascertain the reliability of 0.82which adjudged the instrument reliable. One research question and four hypotheses guided the study. Mean, rankorder, t-test and ANOVA were used to analyse data. Hypotheses were tested at 0.05 alpha level. Hypotheses werenot rejected. Findings showed that display of pornographic pictures, alcohol, peer pressure, inadequate sexeducation, lack of home training among other motivate risky sexual behaviours among in-school adolescents . Finding further showed that gender, age, parental education and school type did not make the respondents dif er intheir responses. The researchers recommend that government should prohibit pornographic displays, indiscriminatesale of alcohol, encourage counselling and parents should monitor their children.