This paper investigates the effects of risk orientation (RO) and social value orientation (SVO) on cooperation and the process of making the decision in a public goods dilemma (PGD). We found in Study 1 that risk-seeking prosocials were more cooperative than risk-averse prosocials in a simultaneous PGD. In Study 2, we found the same effect of RO on cooperation in a real-time PGD. Moreover, we found that risk-seeking prosocials, compared with their risk-averse counterparts, took less time to make decisions and observed fewer preceding cooperation choices before making their decisions. Mediation analysis confirms our model based on the change of K’ index in real-time PGD: The number of preceding cooperation choices being observed by a player mediated the effect of RO on cooperation among prosocials that risk-seekers were more cooperative than risk-averse participants. Our studies illustrate that individual differences such as RO and SVO play an important role in decision processes in PGD that subsequently affects cooperation decisions.