The structure and elemental composition of dry seston were studied in 1989/90 at two sampling stations with different trophic levels in East Lake. The annual average biomass of zooplankton was ca. 1/4 that of phytoplankton. The zooplankton communities were dominated by small protozoans and rotifers. On annual average, dry weight in living plankton constituted 2.5-7.6% of the total dry seston, and plankton carbon only constituted ca. 4.0-9.8 of the seston carbon; C/N ratio of the seston was near to that of phytoplankton, but obviously higher than most. zooplankton; carbon/dry weight ratio was ca. 3/4 that of plankton; ash content of the seston (ca. 45%) was remarkably higher than that of phytoplankton with exception of diatoms. The present results indicate that organic detritus is quantitatively the most important component of the total seston in the ecosystem of East Lake, and living plankton constitute only a small part of the seston ( lt 10%), indicating that in the lake, the turnover rate of the organic detritus from the food web dominated by phytoplankton is remarkably higher than mineralization rate of the organic detritus.