Due to conflicts in the results of previous studies comparing the mental health and personality characteristics of pet owners and non-pet owners, and because of the lack of similar research in the Iranian society, this study was conducted to compare the mental health and personality characteristics of pet owners and non-pet owners. The test group consisted of 400 individuals who referred to the veterinary clinic of the University of Tehran in a 12-month period, and 100 non-pet owners as a control group that were matched based on sex and age with the owners. The International Personality Item Pool (IPIP) and General Mental Health Questionnaire (GHQ- 28) were applied for data collection. Data analysis, using multivariate analysis of variance showed that all groups of pet owners were less open to experience than control group members. Furthermore, mental health problems were observed at a higher frequency in pet owners. Therefore, it was concluded that the causes and conditions of pet ownership in the Iranian culture could be different from those in other cultures.