We report a rare case of psoas abscess formation caused by mucinous cystadenocarcinoma. A 65-year-old women was admitted to our hospital for treatment for iliopsoas abscess. She presented with standing difficulty and her laboratory data showed an increased level of leukocytes. CT scan demonstrated an abscess formation in iliopsoas muscle. Colonoscopy showed an ulcer on her cecum. Although percutaneous drainage was performed on the first day, the abscess relapsed repeatedly. Ileocolectomy was performed on post admission day 29. Abscess drainage continued after the operation, the patient was discharged on postoperative day 34. Pathological examination revealed mucinous cystadenocarcinoma on the cecal tumor. Total 8 cycles of FOLFOX6 was performed as adjuvant chemotherapy. The patient has been survived for 20 months with no recurrence.