The present paper deals with the application of magnetic susceptibility of soil for classification of paddy soils of Tai Hu basin. The results obtained has showed that (1) the magnetic susceptibility X value of paddy soils is much lower than that of their corresponding upland soils derived from same parent material;(2) the X value of the old paddy soils is lower than that of the young paddy soils derived from same parent materials;and (3) the higher.the magnetic susceptibility of the original upland soil, the more remarkable the decrease in the X value of the soil after putting under paddy cultivation. Evident differences of the magnetic susceptibility have been found in profiles of various paddy soils, because different soil moisture regimes and patterns of soil profile may affect the processes of oxidation and reduction of soils, crystallization and decrystallization, leaching and accumulation of ferromanganese minerals, as well as the movement of clay particles which are the principal carriers of secondary ferromagnetic minerals. Therefore, each type of paddy soils in Tai Hu basin has its own unique distribution of magnetic susceptibility in the profile. It may be used as a diagnostic criterion for identification and classification of paddy soils.