The purpose of present research is to study the relationship between job performance and employees’ mental health in one of Iranian natural gas refinery located in city of Jam, Iran. Data collection was conducted based on two major characteristics of job performance and mental health based on questionnaire methods among 42 people. The methodology is descriptive and correlation – type and to analyze the data, Pearson’s correlation coefficient, variances equality tests as well as t-student were utilized. The findings show that there was a significant relationship between employees’ job performance and mental health and any increase in mental health aspects promotes job performance proportionally. In the meantime, there was no significant relationship between employees’ job performance and their gender and there was no significant difference on mental health status between male and female staff. Based on the results, one can conclude that low mental health level among employees can reduce their performance. Managers should use proper methods to decrease the negative consequences resulted from the lack of mental health in workplaces.