PURPOSE: To obtain the subject compound useful as an intermediate raw material for agrichemicals or medicines in a high quality and in a high yield under a mild condition by reacting a pyruvic acid ester with a substituted phenylhydrazine derivative or its salt.

CONSTITUTION: (A) A substituted phenylhydrazine derivative of formula I (R1 and R2 are H, halogen, lower alkyl, nitro, etc.; R3 is H, lower alkyl, acetyl, phenylcarboxyl) or its salt is reacted with (B) a pyruvic acid ester of formula: CH3COCOOR4 (R4 is lower alkyl) to obtain a 2-(substituted phenylhydrazono)- propionic acid ester of formula II. For example, yellowish brown 2-(4- nitrophenylhydrazono)-propionic acid ethyl ester is obtained from p- nitrophenylhydrazine hydrochloride as the component A and pyruvic acid ethyl ester as the component B. The reaction is preferably performed at 25-150°C for 30min to 15hr.