Since SNS has become an important tool for social relationship and information sharing, numerous studies regarding SNS have been conducted in various domains of social science. Among many kinds of SNSs, we have focused on private SNS, which is especially appropriate for communicating with close acquaintances to bond relationship. Firstly, we investigate the difference of communication patterns between public SNS and private SNS to review and clarify key features of private SNS. To address the issues on ideal community size of private SNS, the present study examines some private SNSs limiting the number of friends. With these kinds of SNSs, we secondly clarify whether this function will be useful in managing the users’ relationships for ‘strong ties’ with emotional closeness. As a preliminary study on private SNS, we suggest research framework based on other studies about research methods to analyze SNS usage patterns. Through online questionnaire survey, we expect to attain the results of the research questions regarding private SNS.