This article deals with silicon supplying capacity of paddy soils in south China. 1. The content of SiO₂ in the surface soil extracted by HAc-NaAc (pH 4) for the soils with 5% increase of rice yield due to application of Si-fertilizer was generally less than 9.5 mg per 100 g soil. For the soils with more than 5% increase in rice yield due to application of Sifertilizer, the critical percentage of SiO₂ in straw was usually less than 10% (at ripe stage). 2. The Si-supplying capacity of paddy soils in south China is divided into 3 types: The first type is the soils with low level of Si-supplying capacity, the average available SiO₂ in soil of this type is less than 8 mg, and the SiO₂ in rice straw is about 8.5%. Application of Si-fertilizer to rice plants on the soils of this type may give more than 5% increase of yield. This type includes paddy soils derived from granite, red sand stone and the quaternary red clay occurring on the second terrace of the rolling hills. The second type is the soils with medium level of Si-supplying capacity, the available SiO₂ amounts to 12 mg, while the SiO₂ in plant straw is about 11%. The paddy soils derived from the quaternary red clay occurring on lower slope and valleys of hilly land belong to this type. When they are heavily dressed with nitrogen fertilizer, Sifertiliser might give yield increase. The third type is paddy soils with high level of Si-supplying capacity. This type includes the paddy soils developed on lateritic soils of basalt origin, and those derived from lacustrine deposits and alluvial deposits of the delta regions, generally rice plant gives no response in yield to Si-fertilizer on soils of this type.