The population of Limnodrilus hoffmeisteri Claparède in Lake Taihu (Eastern China) was investigated in 2005 by monthly sampling. The annual average density and biomass of this worm were 3273.75 ind./m² and 4.697 g/m², respectively. Both population density and biomass peaked in February. According to the annual dynamics of the frequency distributions of body length, the species had three generations and reproduced in considerable time throughout the year. The results showed a strong clumped distribution pattern of L. hoffmeisteri but it changed little among seasons. The highest population density and biomass of L. hoffmeisteri were found in Meiliang Bay, Zhushan Bay and the river-mouths areas in the west, while other places of the lake had very low worm density. The key factors regulating this spatial distribution pattern may be nutrient state, types of substrate, food availability and habitat stability.