AIM: To observe the biological characteristics of a species of Plasmodium cynomolgi isolated from a wild-caught, naturally infected monkey Macaca irus (M4) at Pingxiang, Guangxi near the border between China and Vietnam in October 1991. METHODS: An uninfected splenectomized monkey (Macaca assamensis) M6 was inoculated iv with blood from M4. Nine days later, when M6 was found harboring gametocytes at a concentration of 64 per 100 leucocytes, M6 was exposed to the bite of uninfected Anopheles dirus. On day 14 after the level of sporozoites in the salivary gland of An. dirus reached a high peak, the infected An. dirus was allowed to bite M5, a healthy, uninfected monkey (Macaca assamensis). On day 8 following infection, blood was taken from M5 twice a day and examined for malaria parasites. RESULTS: In terms of the appearance of a few rings in blood, the incubation period is 8 days. At a temperature of about 26 ℃ and a relative humidity of 75%, oocysts reached maturity on day 11, and the sporogony was 11 days. The young trophozoites of Plasmodium cynomolgi were indistinguishable from those of Plasmodium vivax. The typical parasites were similar to other simian parasites of Plasmodium cynomolgi. There w re Schüffner’s dots in infected erythrocytes. The schizogony occurred every 48 hours. The mature schizonts had a large number of merozoites, the number being 10- 15. CONCLUSION: The malaria parasite described in the present paper was designated Plasmodium cynomolgi CVH (China, Vietnam and Huang) strain.