Although previous research has indicated that Facebook users, especially young adults, can cultivate their civic values by talking about public matters with their Facebook friends, little research has examined the predictors of political discussion on Facebook. Using survey data from 442 college students in the United States, this study finds that individual characteristics and network size influence college students' expressive behavior on Facebook related to two controversial topics: gay rights issues and politics. In line with previous studies about offline political discussion, the results show that conflict avoidance and ambivalence about target issues are negatively associated with Facebook discussions. Perhaps the most interesting finding is that users who have a large number of Facebook friends are less likely to talk about politics and gay rights issues on Facebook despite having access to increasing human and information resources. Theoretical implications of these findings and future directions are addressed.