Dissertation (MA Demography)Adolescents’ sexual behaviour among students is an issue of concern due to its reproductive health risks and academic development such as school performance. Socio-economic factors that influence this risky sexual behavior have not adequately analyzed. The aim of this study was to identify the socio-economic determinants of risky sexual behaviours among adolescent students and assess the extent of involvement in the risky sexual behaviours. A cross-sectional design using self administered questionnaire was used to collect data from 159 adolescent students from four schools in Kinondoni Municipality, Tanzania. The sample was stratified by sex then systematic sampled. Data was analyzed using SPSS 16 computer programme. Cross tabulation and Chi-square were used to determine the association between socio-economic characteristics and the risky sexual behaviours. Findings showed that 30% of adolescent students were involving in risky sexual behaviours and 11.4% of them were in high risk. The main socio-economic determinants of risky behaviours were; income poverty (p=0.033), age (p=0.000), education level (p=0.000), religion (p=0.033) and internet use (p=0.048). It is recommended that; efforts should be made to reduce poverty and improve quality of sexual and reproductive health services to all adolescents of all sex. Specifically; policy emphasizing sexual and reproductive health education before adolescents become sex active must be established, sexual and reproductive health services should be provided in user friendly ways, students should be assured hostels, food security, transport, contraceptives and sensitized to abstain from sexual intercourse. Similar study could be done in other areas with different socio-economic settings.