B BackgroundStreet children has long been a phenomenal alarming that usually found in bigcities. It is unfortunate that there is very little information and education about sexin the society, especially on sexually-transmitted infection, that could harmchildrens and youth living on the street on their sexual behaviour. Someresearches claim that one of the factors that causes the harmful sexual behaviourof the street childrens is the minimal knowledge on sex education. The purpose ofthis study was to determine the relationship of knowledge about sexuallytransmitted infections with sexual risk behaviors in street childrenMethodThis study uses observational method with cross-sectional method which involved200 street childrens with 200 of them who completed the study. Data collectionwas done by distributing questionnaire on knowledge about sexually-transmittedinfection and sexual behaviour. Data analysis was done by using SPSS for Macwindows version 21.0 and the significance level was set on 0.05.ResultThe chi-square analysis shows that there is relation between knowledge aboutsexually-transmitted infection (p=0,054) of the street childrens with risky sexualbehaviour. There is relation between age (p=0,012), gender (p=0,000) andeducation (p=0,000) with the risky sexual behaviour. Multi-variation regressionlogistic analysis shows that gender is the most dominant factor in affecting streetchildrens’ risky sexual behaviour.ConclusionIt is to be concluded that there is no relation between knowledge about sexuallytransmittedinfection with risky sexual behaviour in street children.