Abstract: An esterification reaction of monomer acid with methanol using p-toluenesulfonic acid as catalyst for the preparation of biodiesel was studied. The process variables that influence the esterification of monomer acid, such as catalyst concentration, molar ratio of methanol to acid, reaction time and reaction temperature, were investigated and optimized. The yield of methyl esters reached to 98.25% under the conditions of reaction temperature of 60 ℃, methanol/acid molar ratio of 3∶1, and catalyst dosage of 6% for 3 h of reaction. The produced biodiesel was found to exhibit fuel properties within the limits prescribed by the latest American Standards for Testing Material (ASTM) and 0^# diesel oil.