The effects of acid rain and several low molecular weight organic acids on red soil pH and exchangeable Al was investigated by simulated leaching experiment with undistributed soil column. The results showed that pH in the 0~10 cm soil depth was decreased by 0.27, 0.44 and 0.08, 0.18, and soil exchangeable Al was increased by 4.43% and 2.38%, respectively, after leached with pH 3.5 and pH 4.5 simulated acid rain, compared with deionised water check, while pH in the10~50 cm soil depth was not changed significantly. pH in the 0~10 cm soil depth was higher within 0.3 unit, and soil exchangeable Al was lower 0.08~0.75 cmol/kg in the citric, malic and oxalic acid treatments than that of in the simulated acid rain treatment, respectively. pH in the 10~50 cm soil depth was decreased by about 0.1 unit, and soil exchangeable Al was increased by 6.99%~12.82 % in 100 μmol/L citric、malic and oxalic acid treatments, respectively, compared with simulated acid rain treatment. pH in the 10~50 cm soil depth was decreased by 0.02~0.83 unit, and soil exchangeable Al was increased by 22.45 %~34.66 % in 10 mmol/L citric、malic and oxalic acid treatments, respectively, compared with simulated acid rain treatment. It imply that low molecular weight organic acids may have a greater threaten in accelerating soil acidification than that by acid rain.