<p>Self-reflection, centered on the introspection and evaluation of one’s thoughts, feelings, and behaviors in relation to self-concerns, occupies a central place in understanding the dynamics of mental health. The dual-factor model of mental health suggests that mental health has both positive and negative dimensions. Nonetheless, the relationship between self-reflection and mental health is a source of continuous controversy. This study is dedicated to thoroughly examining the connection between self-reflection and various mental health indicators and exploring the moderating effects of cultural background and self-reflection measurement tools. A meta-analysis of 39 studies including 12,496 subjects was conducted to determine the magnitude of the relationship between self-reflection and both positive and negative mental health. (1) The random-effect model showed no significant relationship between self-reflection and overall positive mental health or with individual positive indicators, including subjective well-being, life satisfaction, and self-esteem. In contrast, the model showed a significant positive relationship between self-reflection and overall negative mental health indicators, including depression and anxiety. (2) Cultural background moderates the relationship between self-reflection and positive mental health, while different measurements of self-reflection moderate the relationship between self-reflection and both positive and negative mental health. We found that self-reflection was significantly associated with negative mental health but not with positive mental health. Our findings suggest that focusing on self-reflection may offer potential for improving negative mental health outcomes, such as anxiety and depression, particularly when culturally sensitive approaches and appropriate measurement tools are used.</p>