It is imperative to choose some low cost, available and effective ameliorants to improve soil acidity in south China for the sustainable development of agriculture. In this study, four kinds of industrial by-products, coal fly ash, alkaline slag, red mud and phosphogypsum, were chosen to investigate the efficiency and mechanism to ameliorate the acidity of a red soil with indoor incubation experiments. The results indicated that alkaline slag and red mud could decrease the toxic monometric Al, soluble Al and exchangeable Al, increase pH value, exchangeable base cations and ECEC of the soil, and were potential alternatives for lime to improve soil acidity. Moreover, long-term application of alkaline slag and red mud did not intensify the deficiency of Mg and K as that of lime. Coal fly ash showed less effective for ameliorating soil acidity. Even though phosphogypsum could increase the exchangeable base cations and ECEC and decrease the exchangeable Al, phosphogypsum could increase the toxic monometric Al and soluble Al in red soil and thus was not suitable for amelioration of acid surface soil. When the quantities of proton consumption of alkaline slag and red mud added were equivalent to the content of exchangeable acid, the red soil could be effectively ameliorated with pH value rising to 5.81-6.26 and exchangeable Al saturation reducing to 15%, and thus Al toxicity would be eliminated. It is feasible to evaluate the requirement of alkaline slag and red mud in practice to ameliorate soil acidity based on the proton consumption capacity and soil exchangeable acidity.