Psychobiological model suggests that biological and psychological variables have additive functions on exercise adherence. Using the psychobiological model as theoretical framework, the study was designed to examine the effects of self-efficacy, body mass index (BMI), and cardiorespiritory fitness (CF) on Chinese college students' free-time exercise motives. Participants were 208 college students (105 males and 103 females, age range=18-21 years, mean age=20.1 years) enrolling in a large public university in Shanghai, China. Self-efficacy in physical activities was measured using the Self-Efficacy scale and motives for participating in free-time exercise were measured using the Exercise Motivations Inventory version 2 (EMI2) (Markland & Ingledew, 1997). Both instruments were translated into Chinese from English and were validated by bilingual Chinese-American scholars (n=6) in physical education and kinesiology. Cronbach's alpha was .74 or above for self-efficacy scale and all EMI2 scales. Participants' height and weight were recorded with the questionnaires during compulsory physical education classes and their CF levels were assessed using 1,000-meter run test. Hierarchical regression analyses, separately for males and females, were conducted to examine the effects of self-efficacy, BMI, and CF on exercise motives. The independent variables were, in order of entry, age, self-efficacy, BMI, and CF. By entering age, we controlled for it as a possible confounding variable. The analyses showed that for the males, self-efficacy was associated with Appearance motive (DR2=.07, â=.24, P<.05). BMI was associated with Weight Management motive (DR2=.12, â=.32, P<.01). CF level was associated with Revitalization (DR2=.04, â=.20, P<.05), Enjoyment (DR2=.16, â=.37, P<.01), and Competition (DR2=.05, â=.22, P<.05) motives. For females, self-efficacy was associated with Stress Management (DR2=.05, â=.23, P<.05), Revitalization (DR2=.14, â=.33, P<.01), Enjoyment (DR2=.21, â=.42, P<.01), Competition (DR2=.15, â=.45, P<.01), Challenge (DR2=.03, â=.24, P<.05), Social Recognition (DR2=.04, â=.25, P<.05), and Fitness (DR2=.06, â=.25, P<.05) motives. BMI was associated with Weight Management motive (DR2=.06, â=.25, P<.05). CF level was associated with Challenge (DR2=.07, â=.27, P<.05) and Competition (DR2=.04, â=.21, P<.05) motives. These results revealed that perceived self-efficacy in physical activities had broad and direct influences on exercise motives for the female students while cardiorespiratory fitness level seemed to play a role of self-determined exercise motives for the male students. Body dissatisfaction was able to orient exercise for weigh management reasons for both the males and the females. The findings may be fitted within a psychobiological model and recommended that motivation specificity should be considered when developing strategies to motivate college students to participate in physical activities.Keyword(s): college level issues, exercise/fitness/physical activity, health promotion