INTRODUCTION: Age at sexual debut had decreased in the developing countries recently. Few documented studies have looked into the pattern of risky sexual behaviour and associated factors among undergraduate students in Rivers state of recent. This study examined the pattern of sexual risky behaviour of undergraduate in University of Port-Harcourt, Rivers State, Nigeria. METHODS: A descriptive cross sectional survey was adopted and three hundred students were purposively recruited. Data were collected by a self -administered semi-structured questionnaire and analysed using descriptive and chi-square statistics at 0.05 significant level. RESULTS: The mean age of respondents was 21.3 ± 2.8 years; more than half (57.4%) were females. Almost a quarter (24.5%) was each in 200 and 300 level of study respectively and more than a quarter (26.7%) lives alone. Sixty-one percent of the respondents had ever taken alcohol beverage with 36.1% of them were current users. More than half (52.0%) the respondents had either boy/girlfriend and a total of 144 (52.0%) had ever had sexual intercourse; of these 13% reportedly had only one sexual partner in their lifetime; girl/boy friend topped the list of their sexual partner; 48.6% respondents were currently sexually active and 32% used a form of protection during their last sexual activity. The mean age at sexual debut was 17.0 ± 4.5 years. Few (13.4%) have had sex in exchange for gifts and 5.1% of these was with a friend. Higher proportions of respondents who reported lifetime use of alcohol were sexually active (p<0.005). CONCLUSION: Respondents exhibits risky sexual behavior as more had sex without any form of protection. Public enlightenment programmes and targeted behavioral change interventions are therefore recommended.