The aim of this study was to examine the effects of the two cognitive factors proposed by social cognitive theory to be highly influential on behavior (i.e., outcome expectancies and self-efficacy), in addition to optimism and loneliness, on social networking addiction among university students. In the study, 395 Chinese students (145 males, M = 19.05, age range = 17–27 years) voluntarily completed an online, anonymous questionnaire regarding their Internet use. Almost all of the participants (99 %) were found to be using online social networking sites, and findings showed that social networking addiction was strongly correlated with Internet addiction. As hypothesized, more negative outcome expectancies and lower self-efficacy with regard to reducing Internet use were associated with higher social networking addictive tendencies. The results of the path analysis showed that low optimism was an indirect risk factor of social networking addiction through outcome expectancies and self-efficacy, while loneliness was a direct risk factor. The findings provide practical implications to preventive intervention for social networking addiction among youth.