Because of the negative effects of marital infidelity followed to determine the reasons for clinicians and researchers is important. The purpose of this study was to investigate the causes of men marital infidelity. The approach used in the current study was a qualitative research method.To collect data, semi-structured interviews were used. Interview content analysis and categorization codes revealed that the reasons for marital infidelity placed in several categories. Sexual (seeking happiness and freshness due to marriage burnout, having new sexual experiences, sensation seeking, and wife sloppiness), emotional (marital conflicts, crises of life, loss of self, and emotion and though sharing), and external factors (power, having the opportunity to relationship, confidence and support received from friends, attitude or entitlement, de inhibition due to drug use). These categorizations have implications for clinicians and researchers. Therapists working with infidelity should consider these factors in prevention programs and family enrichment. © 2016, Asian Social Science. All Right Received.