The acid values of biodiesel that treated with activated bentonite (1 M H2SO4 in distilled water, isopropyl alcohol and ethanol at 60 ºC for 1 h) was 0.14, 0.21, and 0.27 (mg KOH/g oil), respectively (see in fig. 2). Treated bentonite using ethanol as solvent showed the highest soap adsorption and acid value. Due to low dielectric constant of ethanol increased the space between bentonite layer [5]. Then proton could exchange with the interlayer cation, protonated on Si-O group of the tetrahedral sheet and dissolve octahedral sheet easily. Therefore, the optimize solvent on bentonite activation should be ethanol.