Growth in social network usage came especially from the mobile phone, which was increasingly used from expansion of popularity of smartphone. However, the negative effects of social networks come with repercussions to the users. Smartphone addiction may be a pandemic. For instance, individuals may find themselves unable to concentrate in work place or class due to engagement in the social networks through smartphone. In this study, the exploratory approach attempts to discover the effects of functional characteristics of mobile social network service on decrease of task performance through integrated research frame. At first, we verify the concept of the functional characteristics of mobile social network service, and establish a research model through the concept of cognitive absorption based on the flow theory. Findings reveal that functional characteristics of mobile social network service such as Expert Search, Communication, Content Sharing, and Identity are positively associated with cognition absorption. Furthermore, cognition absorption is positively and significantly associated with smartphone addiction and poor job performance. On the other hand, this study shows that the connection feature among the functional characteristics of mobile social network service is slightly associated with cognitive absorption. Most previous studies in this field have been focused on the positive effects of the social networking service or factors that reinforce social network service. However, in this study, we analyze the negative effects of mobile SNS, and attempt a new theoretical approach to understand the effects of functional characteristics of mobile social network service on decrease of task performance.