Abstract: To study the effects of acid precipition on soil microbial activity, columns containing samples of mountain forest soils ( 0 - 5cm) from Nanning and Liuzhou were leached with a continuous application of 1280mm of simulated precipitation (pH5. 6 - 3. 1). The extent of reduction of soil respiration depended on the characteristics of soil and the pH of acid rain. The nitrification was significantly inhibited by simulated acid rain of pH3. 1. The stimulating or inhibiting effect on organic nitrogen mineralization in soil following continuous treatment of simulated acid rain of pH3. 7 and pH3. 1 depended on the soil characteristics. The effects of simulated acid rain on soil enzyme activities was stimulated, inhibited, or not affected depending on the characteristics of soil and enzymes.