OBJECTIVE: Having sex at early age, having multiple sexual partners, having sex while under the influence of alcohol or drugs and unprotected sexual behaviors are the common characteristics of risky sexual behavior which increases risk of individuals to sexuality and reproductive health problems. Risky sexual behavior is the most common problem in adolescents and young adults which may expose individuals for permanent social, economical, psychological and physical problem. So that this study focus on assessment of risk sexual behavior using institution based cross-sectional study design on 287 randomly selected subjects among Aksum University students. RESULTS: Almost 60% students reported to have ever had sexual activity. Of which 86 (83.5%) and 112 (64.4%) reported having inconsistent condom use and multiple sexual partners respectively. Even though more than half of first sexual intercourse (61.5%) starts due to their desire but still peer pressure and alcohol have significant effect. Similarly the study indicated that a significant segment of students have risk sexual behaviors which increase individuals' risk of acquiring HIV/AIDS. Unless appropriate age and institutional targeted interventions exist, certain behaviors can place the university students at greater risk of HIV infection and sexually transmitted disease.