Based on Greenspoon and Saklofske's (2001) dual-factor model of mental health, we defined adolescents' mental health as comprised of two distinguishable factors: positive and negative mental health. We tested the direct relations between the Eysenck's (1967) Big Two personality traits (Extraversion and Neuroticism) and positive and negative mental health, and explored the mediation effects of perceived school stress in accounting for the relations. Direct and indirect relations were estimated by using structural equation modeling with data from 1,009 Chinese adolescents in a 3-wave study. Results indicated that (a) adolescents' levels of neuroticism showed a positive relation to negative mental health and a negative relation to positive mental health, whereas levels of extraversion showed a negative relation to negative mental health and a positive relation to positive mental health; and (b) adolescents' perceived school stress (PSS) mediated the relation between neuroticism and mental health but not the relation between extraversion and mental health. The findings suggest that school professionals should consider adolescents' personality traits and school-based stress when planning and delivering mental health services. The findings of the relations between extraversion and PSS are also discussed in light of the face culture in China. Impact and Implications: Consistent with prior work suggesting that extraversion is a mental-health-promoting factor, whereas neuroticism is a risk factor, adolescents with high neuroticism were more likely to perceive school stress, which, in turn, related to their mental health. Thus, when planning and delivering mental health services, school professionals should consider taking adolescents' personality traits and school-based stress into account, helping adolescents displaying higher levels of neuroticism cope more effectively, encouraging the adolescents to recognize the benefits of seeking assistance when needed, thus promoting complete mental health among all adolescents.