BaCkgrOU!d: Substance use, more importantly abuse, is one of the many riskfactors thatrnendanger tl; life of yquth. It is perpetuated by inadequate social support, lower socioeconi)rnmic sit , ation,: poor or weak family background, negative peer pressure and lack ofrnalternative amenities. Khat, alcohol and combined use of both substances are widely practicedrnby youth and'young adults in Ethiopia. Literatures indicate that substance use increases thernvulnerability : of users to unprotected sexual behavior leading them to become victims ofrnHIVIAIDS STI, unwanted pregnancy and many other consequences.rnIrnIrnObje~tive: r.~measlre tre magnitude, identifY the socio demographic correlates of substancesrnuse (Khat an Alcohol)' and examine their relation to sexual behavior of Adolescents, youthrnand )ioung a ,ults (15-29) in Mekelle town.rn:rnMethods: A descriptive cross sectional survey was conductedfrom 1110212009 to 171021200Arnamong 535 PWticipants (15-29 of age) together with FGD and in-depth interviews in Mekele,rnthe capital city of the Tigray Regional State of FDR of Ethiopia. The data was coded; entered,rnand analyzedirnrrn' using:SPSS version 15.Focus group discussion, In-depth interview and transectrnwa!kresu!ts ril a!.~o summarized, categorized and incorporated thematically into the thesisrnrepo~t. ':rn, I IrnResult: The study r:evealed that 17.6 %, 42.3% and 13% of the participants do have Khatrnchewing, alcohol drinking and smoking behaviors respectively, though at different level ofrnintakes. Male; 15-19, unemployed and unmarried are the largest share of the users in all kindsrnof substances studied here. Using of alcohol and khat has strong association with risky sexualrnbehavior (~4 0.05). Multiple use of substance i.e. persons who use both khat and alcoholrnconsecutivel~ have very 'strong association with risky sexual behavior (P< 005). Peer pressure,rnreligiosity arlp open dis,cussion with family members contributes to shape the substance usernbehavior of the participants.rn,,rnConJlusion: ~he study finding shows that the most important factors for being exposed to khatrnIrnand alcohol ~se are weak parent-child discussion, peer pressuring for substance use, lowrnreligiOUS commitments and being unmarried. The study also revealed that being exposed tornkhat andalcghol u~e an,d more importantly combined use of both substances in turn leads tornrisky sexual Behavior. Even though ,the consequences o/risky sexual behavior is not the scopernof th,e study] different literatures have affirmed it leads to different reproductive healthrndiseases and)or problems such as HIVIAIDS, STD, Abortion and unintended pregnancy. Notrnwith ~tandin~ to the need for further research on the link between khat and alchol use withrnreprdductive (lealth' problems; the result indicates Youth-specific interventions to reduce thernlikelihood of~xposure of adolescent, youth and young adults to khat and alcohol in order to , Irnprev~nt them from Reproductive health problem, among others.