A few studies have examined the effectiveness of positive psychotherapy for juvenile offenders. There has been no study investigating the effect of positive psychotherapy on Korean delinquent youth. This study was aimed to investigate the effect of brief individual positive psychotherapy on the psychological adjustment of delinquents. Fifteen delinquents participated in three sessions of individual positive psychotherapy focusing on character strengths and gratitude. The Positive and Negative Affectivity Scale(PANAS), Mental Health Continuum-Short Form(MHC-SF), the Rosenberg Self-Esteem Scale(RSES), the Interpersonal Reactivity Index(IRI), the Barratt Impulsivity Test-11(BIS-11), the Aggression Questionnaire( AQ), the Continuous Performance Test(CPT), the Trail Making Test(TMT), and the Stroop test were assessed before and after treatment. It was found that negative affect was decreased and empathy and executive function were improved after treatment. Additionally, the better the baseline working memory and sustained attention, the more the empathic ability improved after treatment. These results suggest that positive psychotherapy may be effective in promoting psychological adjustment and prosocial behaviors in Korean delinquent youth.