This study examined how the personality traits of behavioral inhibition and behavioral activation contribute to the development of anxiety and depression. We used two-wave short-term longitudinal data from 319 students. Data collections were two months apart. Personality traits were assessed using Gray’s Reinforcement Sensitivity Theory: Behavioral Inhibition and Activation Systems (BIS and BAS). After confirming simple correlations, hierarchical regressions were conducted to test how residual changes or unique variances in psychopathology were predicted by the personality traits. Findings revealed that high BIS sensitivity predicted both anxiety and depression, while low BAS sensitivity predicted only depression. These results suggest that hyperactive BIS functions as a predictor for general distress, and that hypoactive BAS functions as a unique predictor for depression.