This study aimed to investigate the relationship between workers’ temperament and their mental health by using TEMPS-A and K10. The “on-job group” (n=289) and the “in-treatment group” (n=54) answered the questionnaire. The results showed that irritable temperament was related to mood disorders attributable to the workplace. Some participants in the on-job group,suffered a decline in mental health despite having no history of undergoing psychiatric consultations. They were unaware of the severity of their condition which was shown in their high K10 scores,and remained untreated. This may aggravate their mental health even further,and carries the risk of their moving on to the in-treatment group,as suffering from atypical depression. They therefore need the active encouragement by people around them to go seek medical assistance.