Adolescents make up a quarter of the world populationand despite being the hardest hit by sexual and reproductive health challenges their sexual and reproductive health (SRH) needs are not fully appreciated andare largely unmet. The challenges are more intense among certain groups, including street children/adolescents based on social, cultural and biological factors. This descriptive cross sectional study was carried out in Dagoretti district of Nairobi, Kenya, to determine the determinants of sexual and reproductive health among street adolescents. Data was collected through interviewsfrom 195 adolescents selected randomly and5 key informants selected purposively representing different players in the street children/adolescents sector in the sub county. The quantitative data was analyzed using SPSS while qualitative data was transcribed, coded and analyzed thematically. The study established that despite moderatelyhigh SRH knowledge among 79% of the participants, 55% of them were involved in high risk sexual behaviour.Majority of the adolescents had sex by the age of 10-15 years (41.9%) with older partners and did not use condoms (74.4%).Adjusting for other factors, male gender (P =0.006), age in years (P =0.037), HIV testing (P =0.011), parents/guardians as a source of SRH information and combination of number of drugs used (P =0.001) were found to be significantly associated with risky sexual behaviour. The study concluded that though street adolescents have high knowledge on SRH their behavior was risky. Further they accessed SRH services and information from informal sources. This study recommends the strengthening and parental involvement in peer education, integration of sensitization of adolescence on drugs and substances of abuse and improvement of health centres as education and service provision centres on ASRH. It further recommends enactment of a comprehensive ASRH policy aimed at providing accurate, age-appropriate and comprehensive sexual and reproductive health education for all adolescents with specific focus on early adolescence (10yrs to 14yrs) and the male gender. It shall inform healthcare policy development and xv implementation to ensure inclusion of street children/adolescents in health care provision especially in SRH issues. Further studies are recommended to understand the gap between knowledge and practice as well as the need to disaggregate data on street children/adolescents by cohorts to ensure appropriate programming for the different age groups.