We have described a new case of accidental intestinal myiasis that had occurred due to Eristalis tenax in Iran. A 4-year-old girl living in rural area near Bajestan city located in the south of Khorasan Razavi province visited the hospital lab with complaints of one live larva in feces and did not have other symptoms, except anal itching. This case had a history of consuming subterranean village water and did not have a history of traveling outside the city or contact with other patients. Conclusion. Based on the morphology characteristic, the larva was identified as "rat-tailed maggot" or larvae fly E. tenax.