Background: Coping with negative emotions are of the everyday life challenges that all individuals encounter constantly. Employing efficient Emotion Regulation [ER] strategies could significantly influence individuals’ quality of life and wellbeing. ER has also been targeted as a core process in the research and treatment of psychopathology. Accordingly, the present study aimed to examine the effects of an ER skills training program on mental health, happiness, and organizational performance in employees. Methods: This was a quasi-experimental study with a pretest-posttest and a control group design. The statistical population of the present study consisted of the employees of the central offices of Bank Mellat [all of which are located in Tehran City, Iran] in April and May 2017 [N=2107]. According to Morgan’s table for sample size, 40 individuals were calculated as the study participants. The experimental group received training for four weeks [two 90-min sessions per week]. Multivariate Analysis of Covariance [MANCOVA] was used to compare the two groups of control and training and eliminate the effect of the pretest. The obtained data were analyzed in SPSS at the significance level of p<0.05. Results: A total of 40 individuals completed the intervention course. The age of the study subjects ranged between 28 and 50 years. The mean±SD age of the study participants in the training and control groups was 26.67±0.49 and 26.89±0.57 years, respectively. The Independent Samples t-test results indicated no significant difference in terms of age between the study groups. Furthermore, the MANCOVA data suggested that after controlling the pretest scores as a covariate variable, the provided emotion regulation training significantly improved the posttest scores of the study subjects [p<0.05, F9.20=-3.295]. Conclusion: ER training could play an essential role in reducing physical symptoms, anxiety, depression, and other mental health conditions by informing a person about positive and negative emotions, as well as accepting and expressing them in a timely manner. The present research findings highlighted the effectiveness of ER skills training on mental health, happiness, and organizational performance of the investigated employees. Accordingly, the significance of ER skills training should be considered in improving mental health, happiness, and organizational performance among employees.