With the development of the internet, people are more convenient to adjust their boundary of friendship through social network sites. To accept or to reject might be just an easy click, but the factors behind the choice are considerable. This paper explores the factors that affect the real social activities by theory of planned behavior (TPB) such as interpersonal boundaries, perceived risk and relationship quality. The empirical result indicates the dimensions in TPB have a significant effect on intention to make friends. However, within the dimensions of mutual commitment, social risk, field and privacy are not significant. It represents that the providers may ponder the difference between practice and online.