Colorectal cancer is a common gastrointestinal cancer. At present, it is recommended to use capecitabine combined with oxaliplatin as adjuvant chemotherapy after colorectal cancer operation. Adverse reactions, such as hand-foot syndrome, nausea, leukopenia and so on, often occurred in the course of such combined chemotherapy, but it is rare to cause abnormal blood glucose. Here was reported a case of 37 years old male patient with colon cancer (no diabetes in the past), who had his blood glucose level continue to rise after five cycles of chemotherapy with capecitabine and oxaliplatin. After the seventh cycle of chemotherapy, the patient stopped capecitabine and oxaliplatin, and got insulin and oral hypoglycemic drugs, and then had his blood sugar level gradually improved. Six months after stopping chemotherapy drugs, the patient could control his blood sugar normal only by metformin.