The major purposes of the present research are to develop a scale to measure unplanned purchase behavior on the Internet, and investigate the antecedents of the Internet unplanned purchase behavior. An empirical study modeled with SEM showed that shopping enjoyment and browsing activities would influence unplanned purchase behavior, while product aesthetics, price promotions, and experienced search would indirectly influence unplanned purchase behavior via shopping enjoyment and browsing activities. The academic and managerial implications of the research were discussed.