We report the first isolation of Anaplasma phagocytophilum in South Korea. A 61-year-old woman presented with a 6-day history of fever, headache, and myalgia. Initial investigation showed neutropenia and thrombocytopenia. We diagnosed human granulocytic anaplasmosis by microscopic examination and serologic testing. The patient recovered fully without antibiotic therapy. The isolate was obtained from the patient's blood by cell culture and mouse inoculation. Its identity was confirmed by an immunofluorescence assay, sequencing of the 16S rRNA gene, msp2 (p44), and ankA genes, and staining and electron microscopy of morulae of A. phagocytophilum in cultured human promyelocytic leukemia HL-60 cells.