<p>The graduate studies stage involves balancing mental well-being and creative demands. However, the relationship between mental well-being and creative ability in graduate students remains a contentious issue, particularly with respect to whether this relationship is linear or nonlinear. This study explored the relationship between mental well-being and creative ability through a longitudinal survey of 1,059 graduate students (<i>M</i>_<i>age</i> = 24.81, 81.6% female) at 15-month intervals via cross-lagged analysis, segmented regression analysis and latent profile analysis. The findings were as follows: (1) graduate students’ mental well-being at Time 1 (T1) positively predicted their creative ability at Time 2 (T2), whereas creative ability at T1 did not predict their mental well-being at T2; (2) a breakpoint between graduate students’ mental well-being at T1 and creative ability at T2 was found at -0.87 <i>SD</i>, below which mental well-being at T1 significantly positively predicted creative ability at T2 and above which mental well-being at T1 did not significantly predict creative ability at T2; and (3) the three mental well-being subgroups at T1 (excellent, moderate, and challenged subgroups) were significantly different in their creative ability at T2. Specifically, the moderate and excellent mental well-being subgroups demonstrated significantly greater creative ability than the challenged mental well-being subgroups did. However, creative ability did not differ significantly between the moderate and excellent mental well-being subgroups. In conclusion, mental well-being may be a necessary but not sufficient condition for creative ability. These findings offer useful insights into supporting graduate student development.</p>