The patient was a 50-year-old male. At the age of 48 years, he had undergone total gastrectomy and right hemicolectomy simultaneously for gastric and ascending colon cancers. Since adjuvant chemotherapy has become common practice for patients with ascending colon cancer, capecitabine was administered for 6 months. One year and 6 months after the surgery, he was diagnosed with recurrence of the ascending colon cancer at the anastomotic site and underwent local colectomy. Considering he was pathologically diagnosed as pT4a, mFOLFOX6 therapy was prescribed as postoperative adjuvant chemotherapy. On the day the 11th course of treatment was initiated, the patient complained of weakness; however, his blood test results showed no abnormalities; therefore, he was followed-up as an outpatient. Three days later, he presented to the hospital with exacerbated symptoms and was diagnosed with rhabdomyolysis due to a marked increase in CK(2,031 U/L). Rhabdomyolysis was determined to be the adverse effect of oxaliplatin because out of all the drugs prescribed to the patient, this condition is listed as a side effect only in oxaliplatin's package insert. Fortunately, outpatient treatment was enough to alleviate rhabdomyolysis. Subsequently, adjuvant chemotherapy was completed without oxaliplatin. The patient has been followed-up without recurrence for 9 months after the surgery.