The social media service has almost become an indispensable part of many people’s lives. Besides the discussion on public issues on the Social network sites, people are posting their personal and mundane daily life events, thoughts, and emotions on SNS that are otherwise inaccessible for other people without social media. Observers of social media have argued that SNSs encapsulate people in an “ambient intimacy” environment since not only can we observe the personal thoughts, feelings, life experiences of our friends by reading their daily updates, but we can also subject our daily rhythm to our friends on SNS by disclosing ourselves. Self-disclosure is a fundamental human social behavior. It refers to people willingly communicating their personal thoughts, feelings, emotions, behaviors or experiences with others verbally (Derlega et al., 1993; Gibbs et al., 2006; Hollenbaugh & Ferris, 2014). Studies investigating self-disclosure online tend to agree that the computer-mediated environment encourages certain people, for instance, more lonely ones or people of insufficient social skills, to meet their expression needs online due to benefits such as anonymity and physical isolation (Baker, 2005; Leung, 2002; Walther, 2007, etc.). These previous studies, however, are mainly addressing self-disclosure within a one-to-one interpersonal communication model (e.g. chatting messenger, telephone, instant message), but are less attentive to the one-to-many self-disclosure on social media, where people are posting their personal affairs to public audiences who are connected to the discloser at different levels of closeness. The authors situate this study in a communication context on social media and intend to explore what kinds of social media users are more willing to present their inner private world in the public eye. Psychological literatures on self-disclosure have identified a series of predictor of self-disclosure: cultural factors, motivational factors, features of the recipients, situational factors, etc. (Ignatius & Kokkonen, 2007). Among the found factors, this study is particularly focusing on one’s social relationship status and personality. We are interested in whether and how their connections to surrounding social circles may correlate with their self- disclosing behaviors to social media audiences, and the mechanism of personality’s impact in the process. This study surveyed SNS users in China. The most dominant SNSs include We Chat, Weibo, Renren and QQ. The survey subjects can be users of any one of the four SNSs. Weibo has over 500 million registered accounts and around 46.2 million daily active users by December 2012. We Chat came into Chinese people’s lives in 2012 and already had over 300 million users by January, 2013. It is primarily an instant message app like whatsapp but rapidly evolved into an important social network service mainly on mobile phones. Renren, the Chinese copy of Facebook, initiated in 2005, is popular mainly among college students and teachers. It has around 160 million registered users and 31 million active monthly users by 2011. QQ was originally an instant message tool similar to ICQ, while the introduction of QQ photo wall makes it share characteristics with other SNSs. The following literature will, first, conceptualize self-disclosure in the context of social media as distinguished from interpersonal and offline communication. Secondly, we will review how the level of social intimacy and loneliness may have an impact on self- disclosure on social media. Finally, we introduce personality as another construct that has been proved to be influential on self-disclosure, social intimacy, and loneliness.