The effects of manure application on the contents and distributions of fractions of organic P in soil and soil particle sizes were investigated in a field experiment,which consisted five treatments of control(no fertilizers),chemical fertilizers,chemical fertilizers plus straw,chemical fertilizers plus green manure, and chemical fertilizers plus pig manure and had continued for 14 years at the farm of Jurong Agricultural Science Institute.The crop rotation of the experiment was summer rice(Oryza Sativa L.) and winter wheat(Triticum aestivum).The results showed that compared with the treatments of control or single application of chemical fertilizers,the combined application of organic manures with chemical fertilizers could significantly increase soil organic P.The contents of soil organic P in different soil particle size fractions were in the following order:0~2 m>2~10 m>50~100 m>10~50 m.Long-term fertilization mainly increased the contents of moderately labile organic P which was a little bit available to plant absorption and accounted for a largest percentage of soil organic P no matter in soil itself or in different soil fractions.The labile organic P was also increased in long-term fertilization but its contribution to plant P nutrition was small since it accounted for only 3% of total organic P in soils.Furthermore,long-term fertilization could decrease the percentage of highly resistant organic P showing that fertilization could also activate the nat ive soil P to improve plant P nutrition.