The purpose of this study was to examine the effect of daily Facebook communications with one's romantic partner on mood and relationship quality. Undergraduate participants from a large Midwestern university who had been involved in a romantic relationship for a minimum of three months completed 14 daily surveys that measured their daily loneliness, mood, relationship satisfaction, and emotional closeness, as well as communications with their romantic partner and all others on Facebook, in-person, and using other forms of communication. Negative Facebook communications with one's partner significantly predicted more daily loneliness, lower daily positive mood, higher daily negative mood, lower daily relationship satisfaction, and lower daily emotional closeness. Positive Facebook communications with one's partner significantly predicted higher daily relationship satisfaction and emotional closeness. This study presents a first step in providing strong evidence for the importance of the effect of Facebook on mood and relationship quality.