The aim of this study was to examine the difference in social skills and psychological wellbeing of adolescents in monogamous and polygamous families. A total of 160 high school students in Sidama community whose age ranges between 14 and 22 years from both monogamous and polygamous families (80 from each family structure) were included in the study. The data were collected using in-depth interview and questionnaire. The results report that adolescents in monogamous families scored more on both social skills and psychological wellbeing. Monogamous parents are more responsive and caring than that of polygamous parents. Adolescents in monogamous families reflected a feeling of happiness, capable in managing their daily activities, sense of confidence in voicing their opinions, positive self-concept and success in their social relationships. Adolescents in polygamous families, in contrast, were found to receive limited interaction and support from their parents; they developed feeling of unhappiness about their families, and lacked trustful and strong relation with their families and others. The study also revealed that adolescents from these families were found to have lower levels of social skills and diminished quality of psychological adjustment. The findings, therefore, suggest that family marriage structure has relation with adolescents’ social development as well as psychological adjustment.