The amelioration effects of black locust leaves, straws of canola, rice and pea on acidity of a red soil from Anhui Province were investigated with incubation experiments. The results showed that the addition of the plant materials increased soil pH to some extent compared with control during 60-day incubation. At the end of incubation, soil pH increased by 0.53, 0.42, 0.30 and 0.26 units as a result of the incorporation of black locust leaves, and straws of canola, pea and rice. The increased extent of soil pH was consistent with the amount of ash alkalinity in the plant materials. The black locust leaves increased soil pH to greatest extent among these organic materials due to the greater ash alkalinity of the plant materials and nitrification inhibiting. Straws of rice and canola increased soil pH mainly through nitrification inhibiting in the soil. Pea straw increased soil pH through ash alkalinity and mineralization of organic N in the plant material. While in the later stage of incubation, the nitrification of NH4+-N from the mineralization of organic N released H+ and decreased soil pH, which reduced the final amelioration of the material on soil acidity. The incorporation of black locust leaves and straws of rice and canola together with pea straw, the amelioration effect of plant materials on the acid soil increased due to the inhibiting of nitrification. Soil pH increased respectively by 0.25, 0.18 and 0.12 units as a result of incorporation of black locust leaves and straws of rice and canola together with pea straw compared with single incorporation of pea straw. We found that incorporation of black locust leaves singly or together with pea straw had greater amelioration effect on acid soils. Thus bio-remediation method can be developed with black locust to ameliorate acidic forest soils in south of China.