Abstract: In this paper, the effect of organic manure on activation to different form ofphosphorus was studied by addition of pig feces, rice straw and cellulose into the soilsin which different form of phosphorus was removed progressively by different reagentsin pretreatment. The results obtained from experiments showed that all P fractionscould be activated by organic manure under aerobic conditions. Pig feces showed a besteffect on the activation and the effect of rlce straw was better than that of cellulose.Under flooding conditions, however. organic manure would enhance phosphorus fixationwhich might be related to a strong adsorption of phosphorus by amorphous iron oxidesbecause a significant activation of phosphorus by organic manure was found againwhen Fe-P, O-P and iron oxides were removed from soils. It was showed by anexperiment of adding artificial Fe phosphate into a P and Fe oxides free soil that 30%of artificial iron phosphate was activated by organ1c manure during two weeks'incubation. The real activation of phosphorus by organlc manure should be higher thanmeasure value due to the masklng effect of iron oxides on P activation.