Abstract: Solid acid catalyst SO₄^2-/ZrO₂ modified by doping Al was prepared by co-precipitation-impregnation method and characterized by infrared spectrum. The activities of fresh, reused and regenerated catalysts were investigated by esterification with glycerol for deacidification of high-acid biodiesel feedstock. The activity of the catalyst SO₄^2-/ZrO₂ modified by 1% Al₂O₃, whatever the catalyst was in fresh or reused or regenerated condition, was better than that of non-modified SO₄^2-/ZrO₂. Al can increase the amount of SO₄^2- on the catalyst, strengthen the combination between S and O, and decrease the loss of SO₄^2- in the esterification process. The conversion of esterification was above 91% under the conditions of atmospheric pressure, 140 ℃ for 4 h, glycerol and fatty acid mole ratio of 6, and SO₄^2-/ZrO₂-Al₂O₃ catalyst dosage (catalyst/oil) of 7%.The acid value of the oil was reduced from 31 mg_KOH/g to 2.8 mg_KOH/g after esterification under above optimum conditions. This low-acid oil is suitable as the raw material of biodiesel.