The production of biodiesel from crude palm oil containing high amount of free fatty acids (FFAs) requires a pretreatment step. FFAs need to be removed by esterification with alcohol in the presence of an acid catalyst in order to prevent soap formation and increase the yield of biodiesel. Sulfuric acid is a very active homogeneous catalyst but it is difficult to be separated from the reaction mixture. To overcome this problem, using an acid heterogeneous catalyst for esterification of FFAs in the pretreatment step is promising. This research, therefore, is carried out in order to investigate and compare the activity of sulfated zirconia and sulfated tin oxide catalysts for esterification of FFAs in crude palm oil. The reaction was performed in a stirred-tank reactor equipped with a reflux condenser. 25 mL of crude palm oil (10%wt of FFAs) was added into the reactor, followed by a mixture of methanol (15-60 mL) and a prepared catalyst (0-2 g). The reaction temperature was maintained at 80 ^oC. The results showed that both sulfated zirconia and sulfated tin oxide catalysts were active for esterification of FFAs in crude palm oil. Sulfated tin oxide had a higher activity than sulfated zirconia. The conversion of FFAs was found to increase with the amount of methanol up to 45 ml and then level off. Similar result was obtained when the amounts of both catalysts were increased. Characterization of sulfated zirconia and sulfated tin oxide catalysts was performed by X-ray diffraction (XRD).