Research on social network analysis (SNA) has been actively pursued. Most SNAs focus on either social relationship networks (e.g., friendship and trust networks) or social interaction networks (e.g., email and phone call networks). It is expected that the social relationship network and social interaction network of a group should be closely related to each other. For instance, people in the same community in a social relationship network are expected to communicate with each other more frequently than with people in different communities. To the best of our knowledge, however, there is not much understanding on such interaction locality in large-scale online social networks. This paper aims to bridge the gap between intuition about interaction locality and empirical evidences observed in large-scale social networks. We investigate the strength of interaction locality in large-scale social networks by analyzing different types of data: logs of mobile phone calls, email messages, and message exchanges in a social networking service. Our results show that strong interaction locality is observed equally in the three datasets, and suggest that strength of the interaction locality is invariant with regard to the scale of the community. Moreover, we discuss practical implications as well as possible applications.