Lyme disease is a vector-borne infection, primarily transmitted by Ixodes ticks, and caused by Borrelia burgdorferi. It has a wide distribution in the northern hemisphere. In Korea, however, only one human case has been reported, although B. burgdorferi was isolated from the vector tick I. persulcatus in the region. A 60-year-old male and a 45-year-old female developed the clinical sign of erythema migrans. Each patients were bitten by a tick four weeks and five weeks, respectively, before entering the hospital. On serologic examination, significantly increased IgM and IgG antibody titers to B. burgdorferi were observed in consecutive tests performed at an interval of two weeks. They responded well to treatment with tetracycline.