This article introduces Cosplay activity first, and then views this activity with the concept of gender. By reviewing the concept and meaning of gender, this article examines if there is the potential in Cosplay to break the gender boundary. Through participant observation and in-depth interview, this article concludes that there is indeed the potential to transgress the gender boundary, but the potential only exists in Cosplay activity; besides, the power of transgression is appropriated from the dominant culture values. Even though, the potential is not deniable. Although gender boundary is not easy to erase fundamentally, the power of revolution still can be seen in Cosplay.