Abstract: An ecosystem restoration project has been carried out in Huizhou West Lake(Guangdong province) since 2004.Submerged macrophytes now dominate the restored area,and water clarity and quality have significantly improved.We investigated the phytoplankton in both the restored area and Pinghu(un-restored area) from June 2008 to May 2009 to reveal the response of phytoplankton to ecosystem restoration of the lake.Results showed that both the community structure and the quantity of phytoplankton in the restored area changed greatly compared to the un-restored area.The annual average biomass and cell density were 0.31 mg/L and 2.75×10⁶cells/L,respectively,which was much lower than for Pinghu(3.27 mg/L and 197.46×10⁶cells/L).In Pinghu,Cyanophyta dominated for most of the year and some species,such as Pseudoanabaena sp.,became the most abundant species.Conversely,species of Cryptophyta,Chrysophytax,and Pyrrophyta dominated in the restored area.In addition,Margalef species richness index of phytoplankton in the restored area was 3.70,significantly higher than in Pinghu(2.68).The present study showed that ecosystem restoration by re-establishing macrophyte dominance is an efficient way to control the development of phytoplankton and improve the aquatic environment of lakes.