Abstract: Monkeys do not express ABO antigens on red blood cells (RBCs), but on tissues, which is an obstacle in ABO typing. In this study we describe a simple and efficient method to type monkeys blood. Rhesus monkeys (n=34) and cynomolgus monkeys (n=16) were typed by the direct and reverse gel system, which has been widely used in clinics in recent years. Based on the results of immunohistochemical staining, we evaluated the feasibility and the interference factors of the gel system to type monkeys. The results revealed that the direct gel system didn’t have a positive report, the fibrinogen and non-specific anti-human antibodies in monkey blood interfered with the reverse gel system in some samples. In accordance with the results of immunohistochemical staining, using clear sera, which were pre-absorbed on normal human type O RBCs, the reverse gel system gave an accurate blood type determination for monkeys. We concluded that the reverse gel system could be used for ABO typing of monkeys, and the fibrinogen and non-specific anti-human antibodies were the major interference factors, which could be eliminated by using clear and pre-absorbed sera.