The invention provides a novel and very efficient method for the preparation of a high-quality lower alkyl, e.g. methyl, ester of a fatty acid in respects of color and odor which is suitable for the manufacture of high-grade soaps even without further purification by salting-out considered indispensable in the prior art processes. The inventive method utilizes a natural oil or fat as the starting material which is subjected to a two-step transesterification with methyl alcohol into a methyl ester of the fatty acid, from which the trace amounts of the colored or chromogenic impurities are removed by admixing an adsorbent. The types of the adsorbent as well as the temperature and the time for the adsorption are important for the effective decolorization. Best results were obtained with a mixture of an activated clay and an active carbon in a specified weight proportion.