Remarkable changes have happened in the communication industry due to the rapid growth of the social networking over the last five years. Adolescent at secondary school level are increasingly accessing and using these social networks in their daily lives. However, the impacts of their access to social media into their sexual behaviour remain underreported. This study was set to explore the relationship between social networks and sexual behaviour. The study was conducted in Morogoro and involved four secondary schools. The study adopted cross sectional research design. Simple random sampling and systematic sampling technique were used to select sample 200 students. Data analysis was done using the Statistical package for social sciences (SPSS) where descriptive and inferential statistics were computed. Index scale was used to gauge students’ sexual behaviour and F-test was used to compare students’ sexual behaviour and their access to social media. The study found that students had risky sexual behaviour: have many sexual partners and were not using condoms consistently. Majority of students have access to social networks and access to social networks was associated with their sexual behaviour. The study recommends that more education be given to parents on the effects of their children access to social networks and their undertaking of risky sexual behaviour so that they can guide and support them on using social networks that does not expose them to unfavourable sexual contents.