Social Network Services(SNS) is a kind of platform services supported by information sharing and evaluation among a large number of users. Thus, loyalty that users continuously utilize and emotionally commit to certain SNS is one of crucial determinants of its success. The current study tried to study how Social Network Service users perceive interactivity and security of its mobile site influence on loyalty toward the SNS. When it comes to methodology, we adopted scales measuring multiple dimensional mobile interactivity, online security, and loyalty from previous literatures. Also, we utilized SPSS 23.0 for factor analysis to get empirical components of interactivity toward SNS and also applied AMOS for Structural Equation Modeling to test hypotheses between suggested factors. As a result, while five dimensions of interactivity toward SNS have been found according to factor analysis such as TWO-WAY COMMUNICATION, ACTIVE CONTROL, and INTERPERSONAL COMMUNICATION, and so forth, only two ones like SYNCHRONICITY and CONTENTS seem to play positive and significant roles in forming loyalty toward SNS. Also, perceived security toward SNS is likely to affect loyalty. Admitting that core benefits that consumers expect to utilize SNS are posting personal experiences and getting sympathy, the level of perceived security which consumers may perceived toward SNS’s application turned out to be essential to determine loyalty to a certain SNS. This suggests SNS providers have to strengthen related services and explanation to security of posted personal information.