Abstract: The present invention discloses a method for preparing biodiesel (Methyl Ester) from any kind of oil, vegetable or non-vegetable oil or used cooking oil. Further, it relates to a method for preparing biodiesel (Methyl Ester) with 100% purity which can be directly used as a fuel in cars, trucks, buses industrial and domestic purpose without any need to blend with any petroleum diesel. The present invention also discloses the biodiesel having improved cold flow properties, flash point and 57 cetane number with reduced exhaust emission where CO2 emits approx. 2.96% v/v and CO emits approx. 0.2 ppm % v/v.