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Phosphorus loadings in sediments play an important role in lake eutrophication and the progress ofits recovery. The phosphorus release is controlled by physical，chemical and biological mechanisms. Alkalinephosphatase catalyzes remineralization of organic phosphorus and then it may be an important factor acceleratingphosphorus cycling in sediments. In this thesis，distributions，properties and function of alkaline phosphatase with depths in sediments of twourban lakes were discussed. Alkaline phosphatase activity(APA)in the sediments of Lake Yuehu decreased withthe sediment depth. APA in sediments of Lake Yuehu was，mainly，inhibited by Phe and L-Cys；and inhibitingability of Phe could be stronger than L-Cys. APA in deeper layer (20-30cm)of sediments was more sensitive tothe inhibitors than other layers，but range of variation in APA was most wide in the subsurface layer (10-20cm).All the facts implied that alkaline phosphatase occurred in various forms (isoenzymes). APA in the sediments withdifferent depths of Lake Donghu responded Phe differently. Reacted with Phe and incubated for one day，theamounts of SRP released by these sediments varied correspondingly. SRP on the overlying water in deeper layers(5-10cm and 15-20cm)of Site D1 was higher than that in surface layer(0-5cm)of the same site，one day afterincubation. Hence，the SRP release resulted，at least partially，from the hydrolysis of some liable organic phosphorusmediated by APA. Alkaline phosphatase in lake sediments plays an important role in the release of internalphosporus loadings and eutrophication. A possible explanation for the sensitivity at deeper layers could be anotheractive region of hydrolysis by alkaline phosphatase from organic phosphorus，which added a new dimension inphosphorus cyling mediated by some biochemical mechanisms.