The total and heterotrophic bacterial distributions, compositions and alkaline phosphatese actibities were analyzed in Lake Soyang from Sep. 1987 to Aug. 1988. The heterotrophic bacteria was small portion, 0.07-2.63% of total bacterial number which ranged from $3.2{ imes}10^{5}$ to $3.2{ imes}10^{6}$ cells/${mu}ell$. The composition of bacterial community was less diverse in summer and at the fish farm site and Peridinium blooming site. Pseudomonas and Flavo bacterium were the dominant genera in all sites. The highest proportion and activity of alkaline phsophatase was appeared in Flavobacterium, while Pseudomonas was the most predominant group.