Although the Korean isolate KI-1 of Toxoplasma gondii has been considered to be a virulent type I lineage because of its virulent clinical manifestations, its genotype is unclear. In the present study, genotyping of the KI-1 was performed by multilocus PCR-RFLP and microsatellite sequencing. For 9 genetic markers (c22-8, c29-2, L358, PK1, SAG2, SAG3, GRA6, BTUB, and Apico), the KI-1 and RH strains exhibited typical PCR-RFLP patterns identical to the type I strains. DNA sequencing of tandem repeats in 5 microsatellite markers (B17, B18, TUB2, W35, and TgM-A) of the KI-1 also revealed patterns characteristic of the type I. These results provide strong genetic evidence that KI-1 is a type I lineage of T. gondii.