Ascariasis is the most common helminthic infection in humans. However, its prevalence has been very low in Korea since the 1990s. Recently, there have been several case reports on intestinal obstruction or pancreaticobiliary disease due to infection with Ascaris lumbricoides in adults. However, cases of ascariasis in children have rarely been reported in Korea. We report a case of ascariasis in a 2-year-old boy who experienced expulsion of an adult ascaris worm from his anus. His mother found the worm in his diaper in the morning. His medical history was nonsignificant for any previous illnesses. There were no specific symptoms, and no abnormal findings were found on physical examination. The worm was pink, elongated, and cylindrical; it was 25 cm long and 5 mm wide. Unfertilized eggs of A. lumbricoides were detected in his stool specimen. He was treated with albendazole and remained asymptomatic at follow-up. As long as the number of immigrants from endemic areas and people returning from overseas trips, and import of agricultural products keep increasing, ascariasis can still occur in Korea. Therefore, it is necessary to raise awareness regarding ascariasis.