A significant body of empirical evidence points to a positive relationship between physical activity and psychological functioning. However, the processes underlying this relationship, as well as the determinants of consistent physical activity, are much less understood. Additionally, social support has also been identified as a possible determinant of experiences and behaviors. Given these current findings, the aim of this study was to examine the role of social support in the relationship between motivation and intensity of physical activity. A total of 226 participants (M = 31.03, SD = 12.71, (Nwomen = 16) participated in the study by accessing an online survey link, which included operationalizations of perceived social support (The Multidimensional Scale of Perceived Social Support (MSPSS)), exercise motivation (The Exercise Motivations Inventory (EMI-2)), and intensity of physical activity (The Godin-Shephard Leisure-Time Exercise Questionnaire). The results demonstrated the moderating role of social support in the relationship between psychological motives and the intensity of physical activity, as well as in the relationship between interpersonal motives and the intensity of physical activity, indicating a significant positive contribution of psychological and interpersonal motives to the intensity of physical activity at moderate and higher levels of social support. The findings also showed a significant role of social support in the relationship between fitness motives and the intensity of physical activity, suggesting a significant contribution of fitness motives to the intensity of physical activity at high levels of social support. Furthermore, the contribution of body appearance and health-related motives, as well as their interaction with social support, did not emerge as statistically significant predictors of physical activity intensity.