Phytoplankton lysis rate in three different eutrophic regions of Lake Taihu was measured by the activities of particle and dissolved esterase, as well as the decay rate of the latter, from August 2009 to October 2010. The present results showed that the particulate, dissolved esterase activity, half life time of dissolved esterase, and cell lysis rates ranged from 0.58-35.15 nmol FDA/(L·h), 0.55-7.59 nmol FDA/(L·h), 7-75 h, and 0.02-0.77 d^-1, respectively. No significant differences were found in the cell lysis rates among the three sampling sites. The significant linear relationship between Chl.a concentration and particulate esterase activities suggests that it is feasible to assess phytoplankton cell lysis rate in Lake Taihu by the esterase assay. Furthermore, Chl.a concentration showed the same pattern with water temperature, a significant difference was observed in Chl.a concentration between Meiliang Bay and lake centre. The strong, negative correlation between Chl.a concentration and lysis rate in Gonghu Bay suggests that phytoplankton biomass was affected by the lysis rate in Lake Taihu.