Background: The aim of this study was to investigate contraceptive non-use and associated factors (socio-demographics, sexual behaviour, internal assets and mental health) among undergraduate university students in 22 countries. Methods: Using anonymous questionnaires, data was collected from 16979 undergraduate university students (mean age 20.8, SD=2.8) from 23 universities in 22 countries. Results: Of the total sample of 16979 undergraduate university students, 7032 (41.9%) reported to have been sexually active in the past 12 months. Of those who had been sexually active, 42.6% reported never (42.7% among male and 42.6% among female students) using contraceptives in the past 12 months. In multivariate regression analysis, among both men and women, younger age, religious affiliation (Hindu; and among women only being Muslim), intrinsic religiosity, and sexually protective behaviour were associated with contraceptive non-use. Lack of internal assets (among men, low life satisfaction and lack of personal control, and among women low personal mastery); among women not having depressive symptoms and among men having PTSD symptoms were associated with contraceptive non-use. Conclusion: Low contraceptive use was found and several factors identified as associated with contraceptive non-use may help guide intervention efforts.