Abstract: A laboratory incubation experiment was carried out to investigate the dynamic effect of the decomposition of rice straw in three paddy soils on dissolved organic matter(DOM) and its chemical fraction including dissolved sugars(DS), dissolved phenols acids(DP) and aromatic compounds. The results showed that the content of DOC increased significantly in the first 7 days of incubation, then no significant changes was observed. Decomposition of rice straw increased DS and DP in the soils. As straw decomposition continued, the percent of DS to DOC decreased while aromatic compounds increased. This suggested that the chemical composition of DOC changed during the period of incubation. The dynamic changes of total dissolved nitrogen（TDN）showed that the decomposition of rice straw induced N immobilization in the soils.