Abstract: Homopolyamino acids and copolyamino acids are prepared by polycondensation of one kind or a mixture of two or more kinds of monoammonium, diammonium, monoamide, diamide or monoamideammonium salts of malic acid and/or maleic acid and/or fumaric acid, one kind or two or more kinds of amino acid being added to said raw materials, respectively, with application of microwaves, the resulting polyamino acids (imide type) being converted to peptide type, homopolyamino acids and copolyamino acids, respectively upon partial hydrolysis. The operation involved in the reaction is simple and the method permits the use of low cost reaction materials. As a result, imide type and also peptide type, homopolyamino and copolyamino acids are produced with uniform quality at a high rate of yield within an extremely short period of time. Accordingly, the method is incomparably superior to those which have been announced in the past.