Abstract: Objective To identify conditions that may improve the successful rate of STZ-induced rat models of diabetes mellitus (DM). Methods 100 male SD rats were randomly divided into control group (n=10) and experimental group (n=90). Rats in the experimental group were treated with intraperitoneal injection of STZ 65 mg/kg once, and were then categorized into succeeded DM model group and failed group. Their body masses and levels of fasting blood glucose (FBG), urine glucose （UG）, urine protein （UP）, urine routine, renal function, liver function, blood lipids and kidney hypertrophy index （KHI） were monitored and compared. Dead rats were dissected to observe diseased organs. Pathological changes of those diseased organs were examined by HE staining. Results DM rat models were established through a single intraperitoneal injection of STZ, with a success rate of 58.89%. During the experiment, 43.33% of rats died. Compared with the rats in the failed group, the DM rat models had significantly higher levels of body mass, food intake, water intake, urine output, FBG, creatinine, blood urea nitrogen, KHI, urinary tract infections, and mortality; but lower levels of total protein, albumin and cholesterol and triglyceride (P<0.05). Nine rats died of pulmonary edema; 19 died of renal abscess. The causes of 11 dead rats were not clear. Conclusion DM rat models can be established through a single intraperitoneal injection of STZ 65 mg/kg, but with high mortality rate. The deaths may be associated with infection, malnutrition, suffocation of lymphatic circulation, toxicity of STZ, and changes in environmental and climate conditions.