Abstract: The effects of simulated acid rain with different pHvalues on the amount of Al released and the change of Al forms of the main acidic soils in southern China were investigated. The experimental results indicated that acid rain had significant effects on the amount of Al dissolved from soils, especially in pH<4.0, but not on the acidification of soils. Acid rain had different effects in various soil types. Highly weathered acidic soils were more sensitive to acid rain. These were closely related to buffer capacity formed by different consumed mechanisms of H~+ and chemical characteristics of Al ions. It is very important that acid rain affected free Al forms of the soils. After acid rain treatment, exchangeable Al increased slightly and the content of moderately labile Al increased significantly. The trend in decrease of organic matter complexed Al was observed. Based on the results obtained in the present work, it was concluded that Al would be transformed to exchangeable or water soluble forms and entered the ecosystem by the effect of acid rain in the long-run. This is a serious problem.

Key words: Acidic soil, Simulated acid rain, Soil acidification, Free aluminum forms