ABSTRACT In this hyperpartisan political landscape, scholars have emphasized the importance of examining how perceptions of political network homogeneity on social media affect political outcomes. However, little research has examined how perceived news credibility mediates the relationship between perceived political network homogeneity and political social media use. Social media platforms aggregate and display news items from many sources, enabling people to make generalized judgments about the overall credibility of news items. Research has suggested that perceived political network homogeneity can bias such collective news credibility judgments. In turn, such credibility perceptions can affect political social media use. Lagged and autoregressive analyses of panel survey data gathered in 2012 and 2016 consistently show that perceived news credibility mediates the positive relationship between perceived political network homogeneity and expressive but not informational political social media use. Perceived political network homogeneity positively predicted news credibility, which in turn increased expressive political social media use. Furthermore, I show that the indirect effects outlined above tend to be stronger among Democrats than Republicans.