Concentration of dissolved DNA, microbial biomass, and consumption of bacteria by heterotrophic nanoflagellates (HNF) and ciliates were examined in a hypereutrophic pond for over 7 months to elucidate the main factors which influenced the release of dissolved DNA. Changes in concentration of dissolved DNA correlated well with both abundance of ciliates ( r = 0.788, p < 0.01) and rotifers ( r = 0.738, p < 0.01). A significant correlation was also found between dissolved DNA concentration and ciliate community ingestion rates ( r = 0.668, p <0.01). These results suggest that consumption of bacteria by ciliates is an important reason for the release of dissolved DNA.