The aim of present article was to examine the extended theory of planned behavior(TPB) model under the assumption that the sufficiency of TPB is still being questioned An extended TPB model was proposed to investigate relations among constructs of the model with the addition of descriptive norm(additive effect) and affective responses to exercise(moderating effect). It was longitudinal in design: A two-wave data collection was implemented. Results of the study demonstrated that the extended model fit the data well: (1)descriptive norm did have a significant effect on intention over and above TPB, (2)affect and affect×intention interaction explained a significant increment of variance in physical activity. And affective response has been found to moderate the intention-behavior relations. This means that the effect of intention on physical activity were dependent upon the level of affective responses to exercise. That is, intentions were better predictors of exercise behavior for those subjects who presented greater positive affective compared to those participants with less positive affective response to exercise. The effect of attitude, subjective norm and descriptive norm(perceived behavioral control) was completely(partially) mediated by intention. The strength of the mediated effect increased along with levels of affective responses(moderated mediation): stronger attitude(subjective norm, perceived norm, descriptive norm)-intention-behavior relationships when affective responses were strong.