To screen spontaneous diabetic mellitus and explore methods for its rapid identification, the basal and inferred levels of blood glucose of 440 overweight, middle- and old-aged cynomolgus monkeys were analyzed. Diagnostic diabetes was further validated by the oral glucose tolerance test (OGTT) and urine glucose. The average level of blood glucose of these cynomolgus monkeys was (3.88±0.98) mmol/L, which was lower than the level for suspected diabetes (5.0 mmol/L). Of them, 56 (12.72%) monkeys were identified with levels of blood glucose greater than 5.0 mmol/L and diagnosed as the diabetic subjects. This population showed impaired glucose tolerance using the OGTT and 39 of the 56 (69.23%) had glucose positive urine. The methods for screening diabetic mellitus used in this study were simple, quick, and limited the harm to animals. However, the incidence of diabetes was higher in these tested monkeys than in the regular human population in China (9.7%), suggesting that these methods are useful for screening diabetic disease in a large population but not suitable for all cynomolgus monkeys.