Users of smrtphone based mobile social network games are rapidly increasing. However, there are few researches for smartphone based mobile social network games. In this paper, we conducted a qualitative study in order to understand the continual usage intention of mobile social network game from indepth interview. As a result, passing time, hedonic valuem social value, challenge/competition, perceived enjoyment, and social interaction were found to have positive effects on continuous usage intention of smartphone based mobile social network game. And network quality, difficulties of game, and social interaction were found to have negative effects on continuous usage intention of smartphone based mobile social network game. This study provides practical suggestions for developers of social network game to invigorate the smart-phone based social network game market, such as improved additional investment for simple game interface, easy game rule, additional interactive services.