University students are expected by the general public to be active in pro-environmental behaviors due to their environmental knowledge and relevant education. However, it is still unclear whether students only educated in environmental knowledge will decide to engage in green behaviors. This study investigates factors that determine university students’ pro-environmental behaviors, which include environmental activism, nonactivism, and private sphere environmental activities. A proposed model for investigating such factors, which include environmental knowledge and attitudes, self-efficacy, self-obligation, behavioral control, and sociodemographic characteristics, was developed. Questionnaire surveys with 337 students enrolled at King Mongkut’s University of Technology Thonburi in the city of Bangkok, Thailand, were carried out. Multiple regression analyses were performed to test the effect of these potential factors on each type of behavior. The results showed that providing only environmental knowledge at a university may not contribute to any kind of pro-environmental behavior. It was found that environmental knowledge and attitudes had a significant effect on students’ nonactivist behaviors. Without positive environmental attitudes, but with environmental knowledge and self-efficacy, students decided to engage in environmental activism. In addition, male students were more likely to engage in environmental activism than female students. Finally, students’ engagement in private sphere green behaviors was attributed to self-obligation, environmental knowledge, and environmental attitudes, as well as grade point average (GPA). Students with a higher GPA were more likely to act environmentally. Therefore, to promote each type of environmental behavior, different environmental education strategies should be developed.