This study used a 2-stage questionnaire survey to explore whether self-regulation by withholding negative emotions (SRWNE) affects mental health and examines further whether cultural fit can moderate the relationship between SRWNE and mental health. The 2-stage studies used data collected from 405 (time 1) and 313 (time 2) full-time staff employed by private and public enterprises in Taiwan. The author tested hypotheses through the use of hierarchical multiple regression. The results showed that controlled SRWNE through external regulation and introjected regulation is significantly associated positively with somatic symptoms, anxiety and insomnia, social dysfunction, and severe depression, whereas autonomous SRWNE through identified regulation is significantly associated negatively with anxiety and insomnia, and social dysfunction. In addition, this study also found that cultural fit may moderate the relationship between SRWNE or introjected regulation and identified regulation and the mental health indicators