The purpose of this study was to identify levels of cognitive distortion, depression, and gambling severity and to identify the influences of cognitive distortion and depression on gambling severity in Koreans with a gambling disorder. Methods: The participants in this study were 150 Koreans with a gambling disorder. Data were collected using self-report structured questionnaires which included individual characteristics, the Gambling Related Cognitions Scale, the Center for the Epidemiologic Studies Depression, and the Problem Gambling Severity Index. Data were analyzed using descriptive statistics, independent t-test, one-way ANOVA, Pearson`s correlation coefficients, and multiple regression. Results: Gambling severity had a significant correlation with gambling related cognitions scale-perceived inability to stop gambling (r=.29, p<.001) and depression (r=.34, p<.001). Among predictors, depression (β=.24, p=.035) and type of housing tenure (β=.26, p=.022) had statistically significant influence on gambling severity. The explanatory power of this regression model was 17.0% (F=3.72, p=.003). Conclusion: The findings from this study indicate that interventions to decrease depression are essential to decrease the gambling severity of Koreans with gambling disorder.