Recently, online group-buying has been a popular business model. It was observed that many characteristics of online group-buying are potential stimuli of impulse buying. Therefore, we target traditional online group-buying and e-coupon group-buying and try to explore the characteristics of online group-buying stimulating impulse buying. Based on the literature review and empirical data collection, we identified five characteristics of online group-buying which may stimulate impulse buying. They are group-buying discount, time pressure, social interaction, perceived shopping convenience and consumption deadline. The data were collected through online questionnaire. The analysis result shows that the five characteristics of online group-buying indeed cause impulse buying. Further, we also explored whether the impulse buying behavior will be moderated in different situations. These moderators include group-buying model (traditional online group-buying vs. e-coupon group-buying), transaction price level, relationship with the group-buying initiator, product type and group-buying experience. The result indicates that the impulse buying behaviors are easier to be stimulated in the following situations: traditional online group-buying, lower transaction price, familiar with the traditional online group-buying initiator, non-food product and more experienced consumers of online group-buying.