Abstract: A method for manufacturing biodiesel comprises the steps of: a) getting an amount of biological oil; b) adding catalysts to the oil; and c) getting the biodiesel. The biological oil is from plants. The volume ratio of the catalysts is between 30% to 70% and the other is the oil. The biological oil is replaced by methyl ester. Or the biological oil is animal oil. The catalyst is alkane or alcohol. Time period for manufacturing the biodiesel is short and cost is low without environment pollution. Thereby it is advantageous than the petrifaction fuel.