This study examines the relationship of adult attachment, social support, and subjective happiness of university students, and confirm the mediating effect of social support in the relationship between adult attachment and subjective happiness. Participants in this study consist of 284 university students enrolled in G city. Data were analyzed using SPSS and AMOS to conduct descriptive statistics, correlation analysis, and a structural equation model. The main findings are as follows. First, Attachment anxiety and attachment avoidance showed negative correlations with social support and subjective happiness. And social support showed a positive correlation with subjective happiness. Second, social support showed a partial mediating effect on the effect of attachment anxiety and attachment avoidance on the subjective happiness of university students. This study is meaningful in providing basic data for educational and counseling interventions that enhance subjective happiness of university students.