Research has been done about “The Use of Two-Step Acid Catalyst at Esterification Reaction in Biodiesel Made from Rubber Seed Oil (Hevea Brasiliensis) and The Characterization”. Decrease in free fatty acid content of rubber seed oil by esterification reaction carried out in two phases with a ratio the volume of rubber seed oil and methanol 5:1 for the first step and 5:5 for the second step …