Mental ill-health has increased among Iranian men in the recent years. Mental health is complexly determined by sociocultural, psychological, demographic characteristics, and some health-risk behaviors such as smoking. This study aimed to explore the association(s) between demographic factors, smoking status, social capital, and poor mental health status in a sample of Iranian men. The data were derived from a survey titled "Urban Health Equity Assessment and Response Tool–2" in Tehran, Iran (n = 11,064). A multistage sampling method was applied in the study. The General Health Questionnaire–28 was used to assess poor mental health status (range = 0-84, scores higher than 23 indicated poor mental health status). The data were analyzed using t test, chi-square test, and multivariate logistic regression. The means of age and family size were 47.14 ± 17.26 years (range = 20-91) and 3.54 ± 1.32 individuals (range = 1-15), respectively. The majority of the participants were employed (57%, n = 6,361). The prevalence of poor mental health was 36.36%, 95% confidence interval (CI) [35.46, 37.26]. The components of social capital were positively associated with poor mental health status. Family size (adjusted odds ratio [AOR] = 0.93; 95% CI [0.90, 0.96]), job status (unemployed vs. employed, AOR = 1.34; 95% CI [1.16, 1.55]), marital status (widowed and divorced vs. single, AOR = 1.09; 95% CI [1.02, 1.17]), education level (illiterate vs. academic, AOR = 1.18; 95% CI [1.09, 1.29]), and smoking status (smokers vs. nonsmokers, AOR = 1.46; 95% CI [1.31, 1.62]) were directly associated with poor mental health status in the logistic regression model. These results suggest that social capital could be an important approach for men to attain suitable mental health and reduce mental disorders. The high prevalence of poor mental health in men merits more attention in mental health policy and program planning.