Clinical psychology trainees often experience emotional difficulties during their clinical training. This study aims to examine the predictive ability of repetitive negative thinking (RNT) for emotional symptoms of clinical psychology trainees. A longitudinal study with 236 clinical psychology trainees was conducted. Before beginning clinical practice (T1), participants responded to measures of emotional symptoms, experiential avoidance, general RNT, and RNT focused on the clinical practice. After two months, participants responded to the measures of emotional symptoms. Bayesian regression analyses showed that the measures of emotional symptoms and RNT focused on the clinical practice at T1 predicted emotional symptoms at T2, whereas general experiential avoidance and RNT did not enter the regression models. These results show that RNT focused on the clinical practice longitudinally predicts emotional symptoms of trainees. Interventions aimed at reducing RNT focused on clinical practice might be efficacious to prevent the increase of emotional symptoms in trainees and to enhance learning during the training.