The aim of this study was to determine estimates of the prevalence and social correlates of physical inactivity among university students in 23 low-, middle- and high-income countries. The International Physical Activity Questionnaire was used to collect data from 17,928 undergraduate university students (mean age 20.8, SD = 2.8) from 24 universities in 23 countries. The prevalence of physical inactivity was 41.4 %, ranging from 21.9 % in Kyrgyzstan to 80.6 % in Pakistan. In multivariate logistic regression, older age (22-30 years), studying in a low- or lower middle-income country, skipping breakfast and lack of social support were associated with physical inactivity. In men, being underweight, being overweight or obese, not avoiding fat and cholesterol, not having severe depression symptoms, low beliefs in the health benefits of physical activity, low personal control and knowledge of exercise-heart link, and in women, not trying to eat fibre, low personal mastery and medium personal control were additionally associated with physical inactivity. Four in each ten students are physically inactive, calling for strategic interventions by relevant professionals in higher educational institutions.