—Location-based Social Networks (LSNs) allow users to see where their friends are, to search location-tagged content within their social graph, and to meet others nearby. The recent availability of open mobile platforms, such as Apple iPhones and Google Android phones, makes LSNs much more accessible to mobile users. To study how users share their location in real world, we collected traces from a commercial LSN service operated by a startup company. In this paper, we present results of data analysis over user profiles, update activities, mobility characteristics, social graphs, and attribute correlations. To the best of our knowledge, this study is the first large-scale quantitative analysis of a real-world commercial LSN service.