This article deals with silicon supplying levels and the response of rice plant to Si-fertilizer on the major paddy soils derived from red earth in South China.1.The effect of Si-fertilizer is negatively correlated with the content of available silica in soils.It seems that the critical value of available silica in paddy soils derived from red earth on quaternary red clay in the southern China may be lower than that in Japan and gores,but higher than that of Taiwan province in China.