Abstract: Purple soil was collected from the National Monitoring Base for Purple Soil Fertility and Fertilizer Efficiency in Beibei, Chongqing and yellow soil from Jinyunshan National Forest Park and used in a greenhouse pot experiment with rapeseed (Brassica napus). Rice husk biochar was applied at 0, 0.8%, 2.0% and 4.0% of the soil weight in each pot; CK, CT₁, CT₂ and CT₃ respectively. The soil nutrient content, soil enzyme activity, microorganism density and plant growth indices were measured after 180 days. The results indicated that both soils were significantly improved by the addition of biochar, the best treatment being CT₃. The organic matter content, total N, P, K, available N, P, K in CT₃ were 1.3, 1.2, 4.0, 1.1, 0.9, 33.1 and 18.0 times those of the CK for yellow soil respectively and 1.4, 1.0, 1.5, 1.1, 0.9, 3.8 and 6.0 times the CK in the purple soil respectively. Compared with the CK, the application of biochar significantly increased the pH in both the purple and yellow soil. Biochar significantly increased the number of two species of soil bacteria, including actinomycetes, and promoted the growth of fungi in the purple soil. The numbers of bacteria and actinomycetes in the CT₃ treatment were increased by 677% and 395% in the yellow soil, while the numbers of bacteria, actinomycetes and fungi in the purple soil were increased by 20%, 88% and 82%, respectively. Invertase and catalase activity were significantly increased by 106% and 30% in the CT₃ treatment, respectively. Similarly, urease and catalase activity were increased by 150% and 130% respectively. Plant heights and biomass of rapeseed in the CT₁ treatment were 4.6 times and 11.4 times of those of the CK in the yellow soil respectively, and 17% and 8% higher than those in CK in the purple soil respectively; other treatments suppressed growth. It was concluded that rice husk biochar could be used as amendment for yellow soil and purple soil in southwest region of China at appropriate application rates.