Abstract: Biochar,prepared out of rice hull through low temperature pyrolysis,was applied into red soil and yellow brown soil at a rate of 20 g·kg-1.Then the soils were incubated in the laboratory to check effect of the application on soil acidity.It was found that the incorporation of rice hull char increased pH in both soils to some extent over the control,mainly by decreasing the contents of exchangeable acid and exchangeable Al,and increasing the content of exchangeable bases and the base saturation.The incorporation of rice hull char also resulted in decline of toxic species of Al obviously in soil solutions,which suggests that the addition of rice hull char could alleviate aluminum toxicity in acid soils to plants.The ameliorating effect of rice hull char was greater on red soil than on yellow brown soil.