Abstract: 250 rhesus monkeys breeding in the house were examined for B.coli.The following is the result of B.coli found in this examination:We obtained 2365 B.coli from the investigation.Among them observe the Trophozoites were 144 individual and the Cyst 144 individual.The Trophozoites measure 30-180 μm in length (averge 108±37.68 μm),and 20-114.4 μm in width (average 57.51±37.98 μm).The Cysts measure 39.6-61.6 μm (average 48.65±6.89 μm) in length and width.To see table 1.The infection rate was found to be 36.4%,with the young group aocounting for 42.86%,the ill group for 42.85%,the quaratined group for 42.50%,the long-term-breeting monkeys for 24.42%,and that its infection rate of 5 and more year old group is lower than that of group of 4 year old below.Of importance to the infection rate of B.coli is the atructure and sanitation of breeding cottages.It is also found that male monkeys are as susceptible as female monkeys and that the B.coli in young monkeys comes down from their while its infection rate is higher than that of their parents.The monkeys could be infected by this B.coli during all seasons,with its higher rate in winter seasons.The parasitic number of 91 positive monkeys was found to be 1-220 individual (Trophozoite and Cyst).To see table 2.The morphology and diagnosis and infected state and so on B.coli on related problems were discussed in this paper.