We examined the extent to which anxious attachment and avoidant attachment predicted loneliness and social self-efficacy among 863 college students. Further, we investigated whether social self-efficacy mediated the relationships between the two insecure attachment styles and loneliness. Pearson correlations and regression analysis showed that anxious and avoidant attachment styles were significant predictors of loneliness and social self-efficacy. Mediation analysis revealed that social self-efficacy fully mediated the relationship between avoidant attachment and loneliness and partially mediated the relationship between anxious attachment and loneliness. Implications for college counseling are discussed, and we propose recommendations for counselors to enhance social self-efficacy and attachment security to decrease loneliness.