Different kinds of social graphs can reveal how users connect and interact with each other. However, due to the limited information that the graph can represent, various types of users’ activities cannot be characterized (e.g., time duration of browsing a profile). An observation from network operators can monitor such information easily, and interpret how users use Online Social Networks better. Furthermore, for ISPs, they have strong incentive to get better understanding of how the traffic pattern between end users and Online Social Networks sites will evolve, and take optimization actions according to the distribution and activities of Online Social Networks users. In this section, we review Online Social Networks user behavior study from the perspective of network traffic analysis.