With the eutrophicated Meiliang Bay and macrophyte-dominated Gonghu Bay of Taihu Lake as test areas, this paper studied the biomass of epiphyte and its effect on submerged macrophyte during the vigorous growth season (May-June) of submerged macrophyte in 2005. The results showed that the biomass of epiphyte attached on macrophyte was higher in Gonghu Bay than in Meiliang Bay, and varied within different macrophyte species. The epiphyte inhibited the photosynthetic rate of submerged plant significantly, which could be up to 91.9% in June, and this effect increased with increasing epiphyte biomass but varied with different host plants.