BACKGROUND: Submucosal fecalith(s) mimicking submucosal tumors of the gastrointestinal lumen are rare. Moreover, accurate preoperative diagnosis of these entities is exceedingly difficult, and the mechanism(s) of their formation remains unclear. CASE PRESENTATION: A 40-year-old woman visited the authors' hospital due to lower abdominal pain and diarrhea. She had previously been treated for endometriosis. Laboratory investigation revealed increased C-reactive protein levels. Abdominal contrast-enhanced computed tomography revealed thickening of the appendix wall and dilation of the small intestine. The patient was diagnosed with paralytic ileus caused by appendicitis, and interval appendectomy was scheduled. She underwent laparoscopic-assisted appendectomy after conservative treatment. Partial cecal resection was selected due to the presence of an elastic mass in the cecum. The final pathological diagnosis was submucosal fecalith, not submucosal tumor. On day 5, the patient was discharged without any postoperative complications. CONCLUSIONS: In cases of appendicitis with fecalith(s) that appear as submucosal tumor(s) on colonoscopy, submucosal fecalith mimicking submucosal tumor should be considered in the differential diagnosis.