Social network services (SNS) provide ways for people to express their thoughts, feelings, and experiences through computer-mediated communication. As SNS become increasingly more popular, studies on individuals’ usage motivations of SNS are conducted to explain the acceptance of SNS and their usage intentions. However, situations in which people become stressed with SNS are also developing. Therefore, it is necessary to reconsider the objectives that people are pursuing when they are using SNS. Using motivation theory and self-disclosure theory, this study in Korea examined the factors influencing self-disclosure and the mediating role of self-disclosure examined in terms of subjective well-being. Based on the results of structural equation model analysis, communication in the SNS had the biggest impacts on self-disclosure; information, entertainment, and privacy concerns also were influential. The results also indicated that self-disclosure caused subjective well-being. This study is one of the first to examine the mediating role of self-disclosure on subjective well-being in social network services.