This study aimed to determine the relationship between the C825T polymorphism in the G-protein ${eta}$3-subunit (GNB3) gene and the response to citalopram in a Korean population with major depressive disorder (MDD). Citalopram was administered for 8 weeks to the 84 MDD patients who completed this study. All subjects were examined using the Structured Clinical Interview for DSM-IV, and the severity of depression was assessed using the 21-item Hamilton Depression Rating (HAMD-21) scale. A main effect of an interaction of genotype with time on the decrease in the HAMD-21 score during the 8-week study period was not found. ANOVA revealed no significant effects of the GNB3 C825T polymorphism on the decrease in the HAMD-21 score at each time period. Although the C825T polymorphism of the GNB3 gene may affect the pathogenesis of MDD, our results do not support the hypothesis that this polymorphism is involved in the therapeutic response to citalopram in Korean patients with MDD.