Purpose: The purpose of this study was to examine the impact of encounters with customer violence on the mental health of customer service workers, and to verify the moderating effect of coworker support. Methods: Workers who indicated that they engaged directly with individuals other than coworkers for more than 25% of their working hours, such as customers, passengers, students, and patients, were the focus of the 6th Korean Working Conditions Survey in 2020. A total of 13,682 people were chosen as the final research subjects, responses from dishonest respondents who had picked "don't know/no answer" or indicated "reject" to pertinent topics such mental health level, were discarded. After adjusting for socio-demographic and vocational characteristics that influence mental health in customer service workers, a hierarchical regression analysis was executed, which incorporated input on customer violence experiences, coworker support, and interaction terms on a step-by-step basis. Results: It transpired that interactions with customer violence had a negative impact on workers' mental health. Additionally, it was shown that workers' mental health status as coworker support increased. Conclusion: This study's limitations include differences in the period the questions were posed, and limitations in interpretation to all workers. And it is difficult to determine the relationship between the frequency of customer violence, occupational characteristics and mental health. Despite its limitations, this study makes an important contribution toward fostering an environment where coworkers can continue to help one another.