Personality traits seem to have an important role in the development, clinical expression, course, and treatment response in eating disorders (EDs). We investigated the effects of an inpatient cognitive-behavioral treatment (CBT) on the measures of temperament and character (Temperament and Character Inventory (TCI)) in 149 consecutive patients with EDs. Baseline assessment included anthropometry, the Eating Disorder Examination (EDE), the Beck Depression Inventory (BDI), and the TCI. Treatment was based on the transdiagnostic cognitive behavior theory and treatment of ED, adapted for an inpatient setting. Treatment effects were tested by paired ANOVA, adjusted for covariates. No effects were found on Novelty Seeking, Reward Dependence, and Cooperativeness. Harm Avoidance (F=18.17, p<0.001), Persistence (F=7.71, p=0.006), Self-Directedness (F=27.55, p<0.001), and Self Transcendence (F=16.38, p<0.001) significantly changed after treatment. Changes in TCI scores were wholly dependent on the changes in BDI and EDE, and independent of ED diagnosis and behavior and of BMI changes. We conclude that in ED, a few scales of both temperament and character are significantly modified by CBT, in relation to changes in psychopathology and depression, independently of nutrition. These results are relevant for future studies based on TCI.