The importance of collaborations across geographical, institutional and/or disciplinary boundaries has been widely recognized in research communities, yet there exist a range of obstacles to such collaborations. This study is concerned with understanding the potential of academic social networking services (ASNS) as a medium or platform for cross-disciplinary or multi-disciplinary collaborations. Many ASNS sites allow scholars to form online groups as well as to build up their professional network individually. In this study, we look at the patterns of user participation in online groups in a ASNS site, Mendeley, with an emphasis on assessing the degree to which people from different disciplinary backgrounds gather in these groups. The results show that while there exists a need for better means to facilitate group formation and growth, the groups in Mendeley exhibit a great deal of diversity in their member composition in terms of disciplines. Overall, the findings of this study support the argument that online social networking, especially ASNS, may foster multi-disciplinary collaborations by providing a platform for researchers from diverse backgrounds to find one another and cooperate on issues of common interests.