Objective To explore the influence of optimistic personality on the sport motivation of college students,and investigate the mediating role of exercise self-efficacy and the gender differences.Methods A total of 520 questionnaires were distributed to students of a university in Shandong by convenience sampling method.The revised life orientation test,self-efficacy for exercise scale and sport motivation scale were used for online survey.Pearson correlation analysis was used to explore the correlations among variables,independent samples t-test was employed to analyze the gender differences of variables,and the mediating effect analysis was used to test the mediating effect of exercise self-efficacy between optimistic personality and sport motivation and the gender differeces.Results Totally 482 valid questionnaires were collected,and the effective rate was 92.7％,including 253 males(52.5％)and 229 females(47.5％).Pearson correlation analysis revealed significant correlations between optimistic personality,exercise self-efficacy and sport motivation in male and female students(all P＜0.01).Independent sample t-test results indicated that there were significant gender differences in exercise self-efficacy(t=2.84,P=0.005)and sport motivation(t=3.40,P＜0.001)among college students,with male students having higher levels than female students.The mediating effect analysis showed that the effect of optimistic personality on sport motivation can be partially mediated by exercise self-efficacy.There were gender differences in the mediating mechanism of optimistic personality → exercise self-efficacy → sport motivation.In males,exercise self-efficacy played a partial mediating role;in females,it played a full mediating role.The mediating effect values were 0.17 and 0.22,accounting for 60.7％and 71.0％of the total effect,respectively.Conclusion Optimistic personality affects sports motivation of college students by exercise self-efficacy.In addition,male students' optimistic personality has dual effects,which can directly stimulate their sport motivation and indirectly enhance their sport motivation by improving their exercise self-efficacy.Female students can enhance their sports motivation mainly by improving their exercise self-efficacy.