Research has shown that religious/spiritual (R/S) beliefs can impact mental health. In addition, individual attachment impacts R/S views and mental health. Still, clinical studies are lacking. This study explores the presence of R/S beliefs and attachment insecurity in psychiatric outpatients and the implication for mental health. Ninety psychiatric outpatients reported their R/S beliefs and were categorized into two groups: religious/spiritual (+R/S) or nonreligious/spiritual (-R/S). The groups were compared on attachment, psychiatric symptoms, religious coping, and life satisfaction. Multivariate linear regression was also performed. The +R/S group had significantly higher religious coping and lower attachment insecurity, depression severity, and social anxiety. Attachment insecurity was associated with negative religious coping. Higher attachment avoidance was associated with lower life satisfaction and higher social anxiety. Many patients in psychiatric care hold R/S views and use religious coping. Their R/S beliefs and attachment characteristics might influence each other and impact their mental illness.