Background: Rotaviruses are the leading cause of acute gastroenteritis in young children worldwide. Rotavirus vaccines have been available in Korea since 2007. Objectives: To investigate the changing pattern of rotavirus genotypes in children with acute gastroenteritis after the introduction of vaccines in Korea Methods: Genotyping of rotaviruses was performed on 140 (12.2%) rotavirus-positive samples collected from 1,147 children hospitalized with acute gastroenteritis at Sanggyepaik Hospital between July 2009 and February 2012. Results: The most prevalent G genotypes were G9 (42.8%, 60 cases), followed by G1 (15%, 21 cases), G3 (14.3%, 20 cases), G4 (7.1%, 10 cases), G2 (6.4%, 9 cases), G10 (2.8%, 4 cases), mixed G-type (7.8%, 11 cases), and non-typeable (3.6%, 5 cases). The predominant types of P genotypes were P[4] (54.3%, 76 cases), P[8] (30%, 42 cases), P[4]+P[8] (14.3%, 20 cases), P[2] (0.7%, 1 case), and P[6] (0.7%, 1 case). The VP7 genes of G9 strains belonged to lineage III. Conclusions: This study provides information on the distribution of rotavirus genotypes after the introduction of vaccines in Korea.