Abstract: The ecological distributions of different microbial physiological groups in West Lake, Hangzhou were studied from 1995 to 1996. The heterotrophic bacteria including ammonifiers, cellulose decomposers, nitrate reducers and denitrifiers were rich in Yuhu Lake, where the water was eutrophic; while autotrophic bacteria, shch as ammonia oxidizers and nitrite oxidizers, were more common in Xiaonan Lake where the water quality was relatively good. Ammonifiers and cellulose decomposers had the negative relations with ambient temperature, no matter whether they were in the water body or in the sediment. Compared with historical data, it was founded that the heterotrophic bacteria and coliform groups were decreased significantly after comprehensive treatment of West Lake in 1986, but recently they have increasing trend. After determining 78 heterotrophic strains isolated in water body in Apr. 1996. The authors found that Pseudomonas and Enterobacteriaceae were the dominated species; in 117 heterotrophic strains isolated from the sediments in Oct. 1995 and Mar. 1996, about 50% were belonged to Bacillus and about 24% were Enterobacteriaceae. According to the data supplied by co-operators, it was founded that ammonifiers, cellulose decomposers, nitrate reducers and denitrifiers in the water body had more constrained relations with total nitrogen than with total phosphorous. It was also founded that these bacteria had the negative relationship with the densities of phytoplankton and zooplankton.