Although the degree of self-disclosure or anonymity is usually self-manageable and it is regarded as a hallmark of the web, the role of self-disclosure is little known, especially in the online social network context. Studies about social identity and behaviour have uncovered a significant impact of self-disclosure on online communication (e.g., the social identity model of deindividuation effects). In contrast, prior research on online social networks has surprisingly overlooked the role of self-disclosure in network formation. The reason is that the social network approach overemphasises on the structure of social relations. However, this paper argues that it is also important to consider about non-graph-theoretic attributes because they might play a confounding role in network formation. The paper thus focuses on the degree of self-disclosure of individual actors, and reveals how they influence the probability of reciprocity and transitivity in network formation. To examine the relationship, this study involves to collect data from LiveJournal, and analyses it by using an exponential random graph model (ERGM) method.