NOVELTY - Preparing biodiesel using Melia azedarach L. seed oil comprises (a) pre-treatment stage: extracting and de-acidifying dried M. azedarach L. seed oil by solvent; (b) interchange esterification reaction: adding absolute methanol or absolute ethyl alcohol, standing; and (c) post treatment stage for manufacturing biodiesel: getting upper layer liquid containing biodiesel phase, distilling, absorbing stirring, and removing silica gel or active, and drying with anhydrous sodium sulfate or activated alumina, and removing anhydrous sodium sulfate or activated alumina.    USE - The process is useful for preparing biodiesel using M. azedarach L. seed.    ADVANTAGE - The process solves the problem that the existing process causes environmental pollution and has low percent conversion. The process has wide applicability, good effect, and high purity quotient and also has good multipurpose use effect.    DETAILED DESCRIPTION - Preparing biodiesel using M. azedarach L. seed oil comprises (a) pre-treatment stage: extracting and de-acidifying the dried M. azedarach L. seed oil by solvent so that acid number is reduced to less than or equal to 1 mg potassium hydroxide (KOH)/g to reserve; (b) interchange esterification reaction: using M. azedarach L. seed oil with lower acid number as raw material, adding absolute methanol or absolute ethyl alcohol of 15%-25% of the oil weight and potassium hydroxide of 1.5%-2.5% of the oil weight to have interchange esterification reaction, standing for layering so as to obtain upper layer liquid containing biodiesel phase and lower layer liquid containing glycerin and solvent phases; and (c) post treatment stage for manufacturing biodiesel: getting the upper layer liquid containing biodiesel phase, distilling under normal atmosphere to remove most of solvent, then absorbing ester phase with silica gel or active carbon under stirring state, and removing the silica gel or active with vacuum filtering, at last drying with anhydrous sodium sulfate or activated alumina, and removing anhydrous sodium sulfate or activated alumina with vacuum filtering to obtain biodiesel.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram for preparing biodiesel using M. azedarach L. seed (Drawing includes non-English language text).