The nonstructural protein 4 (NSP4) of rotavirus encoded by gene 10, plays an important role in rotavirus pathogenicity. In this study, NSP4 gene sequences of human rotaviruses circulating in Seoul, Korea between March 2004 and April 2005 were determined. The nucleotide sequence data indicated that the NSP4 genes of human rotavirus Korean isolates were 750 or 751 bases in length and encoded one open reading frame of 175 amino acids with two glycosylation sites. The NSP4 of Korean isolates exhibited amino acid sequence homologies between 59.4% and 98.9%. The NSP4 of CAU4 and CAU15 showed a high degree of amino acid sequence homologies with NSP4 genotype A viruses, but the NSP4 of CAU5, CAU6, CAU11, CAU14, CAU16 and CAU22 exhibited a high degree of amino acid sequence homologies with NSP4 genotype B viruses. Interestingly, CAU3 and CAU7 showed low degree of amino acid sequence homology with those of currently described NSP4 genotypes A to D and belonged a distinct lineage on the phylogenetic tree. These findings suggests that distinct NSP4 type was circulating among human rotavirus strains in the local community of Seoul and raising intriguing questions regarding possible explanations for new genotype.