Massively Multiplayer Online Role-Playing Games (MMORPGs) provide lifelike virtual environments, where players can freely behave while escaping from reality. Players can conduct a variety of activities including combat, trade, and chat with other players like in real world. Due to the development of the Web and Internet, numerous players have enjoyed MMORPGs, and it offers a big opportunity for conducting large-scale researches to understand human behaviors and social networks. Since online world is similar with real world, players can construct their identities independently of their real life. They can
freely choose the appearance of avatars, and even decide their opposite gender. This leads to an interesting phenomenon, "gender swapping", which refers to players choosing avatars with genders opposite to their natural ones. This phenomenon was first observed several decades ago, and there is a line of research investigating who enjoy this phenomenon, and why they swap genders in MMORPGs. However, due to limited data access, those studies have been done in a relatively small-scale by conducting online surveys, which leaves the risk of sampling error.
In this thesis, an attempt is made to understand gender swapping using the entire data of Fairyland Online, a globally serviced MMORPGs. The results not only show which kinds of people participate in this phenomenon, but also report the behavioral patterns observed in players of this game during social interactions, both when playing as in-game avatars of their own real gender, or gender-swapped. Lastly, we show differences of structural patterns in social network against possible four gender combinations from two real genders and two in-game genders. This thesis also discusses the effect of gender role and self-image in virtual social situations, and the potential for this study to improve MMORPG quality and increase our understanding of social networks.