There is substantial evidence that participating in regular physical activity across the life span is linked to improved physical and mental health (USDHHS, 2000), but the physical activity levels of young adults, particularly college students, have decreased in recent years (ACHA, 2001). This is a time of critical importance in developing a lifestyle that will likely persist into the adult years. If we are to encourage college students to adopt active lifestyles, it is important to understand the influence of psychosocial factors on their physical activity choices. According to social cognitive theory (Bandura, 1986, 1997), self-efficacy and social support are two critical psychosocial factors that are associated with physical activity. To date, however, little attention has been given to the roles of the subdomains of these factors on college students' physical activity behaviors. Therefore, the purpose of this study was to examine the relationships among self-efficacy, social support, and physical activity levels. Participants were 193 undergraduate students (111 women, 82 men; M age = 21.15 years, SD = 3.10) recruited from kinesiology courses at a southeastern university. They completed questionnaires assessing two aspects of self-efficacy: making time and resisting relapse (Sallis et al., 1988), social support from family and friends (Prochaska et al., 2002), and self-reported physical activity (IPAQ; Craig et al., 2003). Data were analyzed using correlations to assess the relationships among the variables and hierarchical regression analyses to predict levels of walking, moderate and vigorous physical activity. Specifically, demographic variables were entered in the first block of the model, followed by social support in the second block and the efficacy variables in the third block. Correlational analyses revealed a pattern of positive correlations among the psychosocial factors. There were also positive associations between self-efficacy, both making time and resisting relapse, social support from family and friends, and students' moderate and vigorous physical activity. Hierarchical regression analyses revealed that self-efficacy for resisting relapse was the only significant predictor for walking (R2= 4.3%). For moderate physical activity, family social support, friends' social support, and self-efficacy for resisting relapse were positive predictors, accounting for 2.6%, 4.0%, and 5.0% of the variance respectively. Friends' social support and self-efficacy for resisting relapse were positive predictors for students' vigorous physical activity, accounting for 10.5% and 11.9% of the variance respectively. These findings provide insight into how specific subdomains of social support and self-efficacy influence physical activity patterns.Keyword(s): exercise/fitness/physical activity, health education college/univ, research