A 57-year-old man presented with abdominal discomfort. A computed tomography (CT) scan revealed a tumor, with a maximum diameter of approximately 5 cm, in the transverse mesocolon near the splenic flexure as well as a small nodular shadow suggestive of peritoneal dissemination on the greater omentum. Fluorodeoxyglucose (FDG)-positron emission tomography (PET) showed marked accumulations of FDG at the same sites. Laparoscopic examination revealed an elastic hard tumor, with a maximum diameter of slightly over 5 cm, at the posterior sheath of the transverse mesocolon and a small nodule on the greater omentum with apparent dissemination. Since radical surgery was considered to be difficult to perform, we only resected the disseminated nodule for diagnostic purposes. The final pathological diagnosis was biphasic- type (mixed epithelial and sarcomatoid type) malignant mesothelioma arising from the peritoneum. Approximately 20 days postoperatively, the patient received combination therapy with pemetrexed and cisplatin with a 3-week interval between the courses. Image assessment after completion of the third course revealed enlargement of the tumor mass and worsening of the peritoneal dissemination. Therefore, the treatment was switched to paclitaxel, which has been reported to be effective as a second-line therapy. The drug was scheduled to be administered on days 1, 8, and 15. However, after the first course on day 1, the patient's condition gradually deteriorated and he subsequently died.