It is well documented that regular physical activity is important to healthy lifestyles. Research has demonstrated that self-efficacy is an important motivator to help individuals maintain physical activity behaviors. Self-efficacy refers to beliefs about one's capabilities to learn or perform behaviors (Bandura, 1997). Individuals reporting high levels of self-efficacy are more likely to try new behaviors, put forth more effort on those behaviors, experience greater enjoyment, and persist longer than those who report low levels of self-efficacy. Such relationships, however, have not been extensively investigated in the context of college physical activity classes. Therefore, the purpose of the present study was to extend previous research by using structural equation modeling (SEM) to examine the relationships between students' self-efficacy and their perceived effort, enjoyment, and boredom in college physical activity classes. Participants consisted of 384 students (231 males; 150 females) who were enrolled in university activity classes including weight training, volleyball, and running. They completed questionnaires assessing their self-efficacy and perceived effort, enjoyment, and boredom in the class. All measures were derived from instruments that demonstrated acceptable validity and reliability. Competing models were tested: one in which the effects of self-efficacy on enjoyment and boredom are fully mediated by effort put forth in the class, and another where the effects were only partially mediated. The test of the fully mediated model was relatively poor: chi-square (51) = 278.31, p < .001; RMSEA = .11; CFI = .85; IFI = .85. However, the test of the partially mediated model provided a better fit: chi-square (49) = 178.44, p < .001; RMSEA = .08, CFI = .92; IFI = .92. Furthermore, the partially mediated model was statistically superior to the fully mediated model: change in chi-square (2) = 99.87, p < .001. Results further indicated that self-efficacy was significantly related to effort (b = .46, p < .001), enjoyment (b = .68, p < .001), and boredom (b = -.46, p < .001), while effort was significantly related to enjoyment (b = .14, p < .01), but not boredom (b = -.01). In all, the model explained 21% of the variance in effort, 57% in enjoyment, and 22% in boredom. An important finding of the study is that effort mediated the relationship between self-efficacy and enjoyment, thereby further highlighting strategies to increase students' self-efficacy. Additional implications for theory and practice are advanced. Keyword(s): college level issues, exercise/fitness, physical activity