It is well documented that the physical activity levels of young adults have declined below the recommended guidelines on health. Since positive experiences in physical education (PE) could influence individuals to adopt physically active lifestyles, studying different motivation types (motivational regulations) in university PE is warranted. Guided by the self-determination theory (SDT), the main purpose of the present study was to investigate the differential relationships among social environments (i.e. autonomy support, self-reference, and cooperative learning), basic psychological needs (i.e. autonomy, competence, and relatedness), and motivational regulations in university PE courses. Hong Kong university students (N = 219) aged 18–26 completed questionnaires that assessed the SDT variables in PE and exercise behaviours. Multiple mediation analyses showed that all three social environments had positive indirect effects on intrinsic motivation and identified regulation through all three psychological needs, except for indirect effects of autonomy support through autonomy. Moreover, autonomy support had a positive indirect effect on introjected regulation through relatedness, and cooperative learning had a negative indirect effect on amotivation through autonomy. Overall, relatedness was the strongest mediator. Finally, intrinsic motivation and identified regulation were positively associated with enjoyment and intention for future participation in the PE activity. The results are consistent with SDT assumptions and expand the literature on the differential effects of social environments on motivational regulations in university PE. Implications on teaching strategies and future studies are discussed.