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A process for producing a phenylalanine derivative which has a quinazolinedione ring and is represented by the formula (5), which comprises reacting an acylphenylalanine derivative represented by the formula (1) with a reagent for carbonyl group introduction and an anthranilic acid derivative to form an asymmetric urea intermediate, converting this asymmetric urea intermediate to a quinazolinedione compound in the presence of a base, and N-alkylating the resultant quinazolinedione compound at the amide group of the quinazolinedione ring with an N-alkylating agent. This process is suitable for the industrial production of the phenylalanine derivative containing a quinazolinedione skeleton, which is a compound highly useful as a medicine having integrin &agr;4 inhibitory activity. In the formulae (1) and (5), R1 represents substituted phenyl, etc.; R2 represents alkyl, etc.; R3 represents dialkylamino, etc.; and R4 represents alkyl, etc.