The patterns and determinants of physical inactivity among the Chinese youths are unknown. This study assessed the prevalence and predictors of physical inactivity among students in a Hong Kong university. A cross-sectional survey of year 1 and year 3 Chinese undergraduate students in 1997, using a structured, self-administered questionnaire was carried out. Questionnaires were returned by 64 % (1189/1849) of the students. Thirty-one percent of the respondents did not participate in physical activity. Being female, not a university resident, studying in the Faculty of Arts and rating current health status as poor or very poor were predictors of physical inactivity. No time and no interest were the most common reasons for non-participation in physical activity among the students. This study showed that about one-third of Chinese university students are physically inactive and would gain health benefits from organized intervention. Awareness among the students about the risks of physical inactivity should be enhanced and efforts made to increase physical activity should be reinforced. Factors identified as predictors of physical inactivity should be taken into account in the design of intervention.