A 42-year-old Japanese woman, who resided in Indonesia suffered from watery diarrhea. As soon as she returned to Japan, she had a medical examination at our hospital. Oocysts of Cyclospora cayetanensis were isolated from her stool on the 14th day. Treatment with 1.6g/day sulfamethoxazole/trimethoprim combination for 1 week was effective. Cyclosporiasis is a of newly-emerging infection and causes group infection or traveler's diarrhea. Cyclosporiasis should be suspected in patients with diarrhea who have returned from the endemic areas to Japan.