Background and purpose: The pace of population aging is fast, so maintenance of mental health in elderly is an important issue. This study aimed to assess mental health in older adults and some relating factors. Materials and methods: In a cross sectional study, 400 old people were selected by multi-stage sampling in Tehran 2014-15. Data was collected using General Health Questionnaire (GHQ-28) and the lifestyle questionnaire. Multiple linear regression model was used to determine the adjusted association between demographics and underlying factors with mental health. Results: The mean age of participants was 67.7±7.63 years and mean score for their mental health was 21.82±11.37. According to regression model after adjusting other covariates, some variables, including gender, age, education, employment, life satisfaction, motor-physical limitations, and using rehabilitation instruments were the predictors of participants’ mental health (P˂ 0.05). Conclusion: This study revealed that physical health in elderly has a key role in their mental health. Motor-physical disability is one of the main predictors of mental health among old people. Physical activities and health and also employment situation should be considered in interventions designed to promote mental health in older population.