Abstract: Organic phosphorus in sediments can be converted into inorganic phosphorus, which may accelerate lake eutrophication process. Sectional sediment samples were collected in Lake Chaohu, organic phosphorus in sediments were extracted by Ivanoff method, and alkaline phosphatase activity in sediments were determined. The hydrolysis effects of alkaline phosphatase on NaHCO₃ extracted Po (NaHCO₃-Po), HCl extracted Po (HCl-Po) and NaOH extracted Po (NaOH-Po) in sediments were studied. The results indicated that Po content at C14 sampling station in the eastern half of the lake was higher than that at C4 sampling station in the western half of the lake. The proportion of NaOH-Po, HCl-Po, NaHCO₃-Po and Residual-Po in total organic phosphorus was 41.70%, 12.82%, 11.05% and 2.22%, respectively at C4 sampling station, 43.75%, 19.00%, 6.12% and 4.22%, respectively at C4 sampling station, and the concentrations of different forms of organic phosphorus were in the order of NaOH-Po>HCl-Po>NaHCO₃-Po>Residual-Po. The alkaline phosphatase activity at C4 sampling station was higher than that at C14 sampling station due to high eutrophication level in the western half of Lake Chaohu. NaHCO₃-Po, HCl-Po and NaOH-Po could be hydrolyzed by alkaline phosphatase, and the hydrolysis contents of various organic phosphorus in surface layers at C4 and C14 stations were significantly higher than those in deep layers, indicating that the bioavailability of organic phosphorus produced by human activities were higher. Indeed, the hydrolysis ratio of NaHCO₃-Po was highest with 65.78%-69.47% averaged values due to its simple and small molecular compounds.