Privacy concerns about peer’s disclosure of one’s information (PCAPD) loom as social networking sites (SNSs) getting popular. PCAPD is different from and more complex than privacy concerns in e-commerce contexts. Based on the Communication Privacy Management theory, we propose that decisional control helps reduce a SNS member’ PCAPD, and that this effect is contingent on two factors – the overlap between the discloser’s social network and that of the disclosed, and information exclusivity. Laboratory experiments were carried out to test the hypotheses. The results showed that decisional control reduces a member’s PCAPD. When the discloser’s social networks overlaps with that of the disclosed, the effect of decisional control on PCAPD is stronger than when the two do not overlap. In addition, information exclusivity increases PCAPD. This study extends privacy research to the online social network context. It also suggests pragmatic strategies for SNSs to alleviate members’ privacy concerns.