Purpose: The purposes of this study were to determine the moderation effects of affective attitude on the effects of cognitive attitude and intention on leisure-time moderate-to-vigorous physical activity (MVPA). Methods: A total of 2100 undergraduate students completed validated instruments measuring their affective and cognitive attitude, intention to do MVPA, and leisure-time MVPA. Hierarchical regression analyses and Hayes' Process program (model 1 and model 58) were used to address the research questions. Results: The results showed that affective attitude significantly moderated the effects of cognitive attitude on MVPA. It suggested that when affective attitude was negative, the effect of cognitive attitude on MVPA was not significant; when it was positive, the higher the value of affective attitude score, the larger the effects of cognitive attitude on MVPA. The results also showed that affective attitude significantly moderated the effect of intention on MVPA and the indirect effects of cognitive attitude on MVPA through intention. It suggested that the higher the value of the affective attitude, the larger the effects of intention on MVPA and the larger the indirect effects of cognitive attitude on MVPA through intention. Conclusions:These results indicate that the moderating role of affective attitude in behavior change is important and should be considered for future theory development on the relationship between attitude and behavior. Practically, it suggests that people's affective attitude should be first understood and addressed when designing PA promotion programs.