The various forms of nitrogen in 25 rivers surrounding Lake Taihu as well as in some typical lake zones such as Meiliang Bay and East Lake Taihu were analyzed during the hydrological year of 2009-2010. Furthermore, the nitrogenous self-purification capacity of Lake Taihu was studied in combined with the investigation of water flow, cyanobacteria salvages and aquatic product outputs. In the whole hydrological year, the inflow and outflow fluxes of total nitrogen (TN) were 7.00 x 10(4) t and 4.01 x 10(4) t, respectively. About 3.02 x 10(4) t and 0.20 x 10(4) t nitrogen in water body were removed by denitrification and sediment adsorption during this hydrological year, respectively, suggesting a strong nitrogen self-purification capacity of Lake Taihu. The potential denitrification is stronger in western Lake Taihu (e.g., Meiliang Bay) than that in eastern Lake Taihu (e.g., East Lake Taihu), and is stronger in summer than that in other seasons. Thus, the nitrogenous self-purification capacity plays an important role in nitrogenous transference and transformation in Lake Taihu.