Bidding strategy in online auctions, as a sort of strategic behavior, can help bidders to get what they want more efficiently and effectively. It receives much attention in many researches. However, the determinants of bidding strategy adoption still remain unclear. In this study, we investigate the role of social network in bidding strategy adoption using real transaction data from an online P2P lending market. The analyses reveal that 1) bidding strategy tends to be homogeneous in different online social networks. 2) Joining an online social network does not change the bidding strategy adoption behavior significantly. 3) The size of social network will affect bidding strategy adoption and smaller ones are more homogeneous than bigger ones. 4) In a social network, bidders with different roles have different preferences on bidding strategies. Our findings can be considered as important empirical evidences for theories about social influence and human behavior.