A method for determination of isoflavone in extract of soybean by highperformance liquid chromatography(HPLC)is described.The optimum hydrolysis condition of extract of soybean was obtained by using the orthogonal design method and the analysis of variance,the analytical condition of HPLC was also established.The method is rapid,sensitive,reproduciable and provides a recovery of more than 99% with RSD less than 3%.