Leiomyosarcoma (LMS) of the small intestine is a rare tumor, accounting for about 1% of all malignant mesenchymal lesions in the gastrointestinal tract. Since small bowel tumors are initially asymptomatic and nonspecific, delayed diagnosis and treatment are common. We found that a 44-year-old male patient who came in for lower abdominal pain had partial obstruction in the small bowel. Multiple ascites and ileal tumors involving peritoneal seeding were observed from his abdominal computed tomography. He was diagnosed as epithelioid LMS involving peritoneal transition after surgical resection, and the outpatient department has planned for a conservative therapy with observation. To the best of our knowledge, ileal epithelioid LMS accompanying a huge omental mass, with a size of 18 cm in dimension, and peritoneal seeding has not yet been reported in Korea. We report this rare case with literature review.