In a previous paper, we showed that 5-aminosalicyl-L-aspartic acid (5-ASA-Asp) has much greater deconjugation efficiency in the cecal contents than does 5-aminosalicyl-L-glutamic acid (5-ASA-Glu). To explore a reason for ineffective deconjugation of 5-ASA-Glu, structural analysis of the conjugate was performed. Aromatic acyl-L-glutamic acid derivatives, N-benzoyl-glumatic acid (BA-Glu), N-(2-hydroxybenzoyl)-glutamic acid (SA-Glu), N-(3-aminobenzoyl)-glutamic acid (3-ABA-Glu) and N-(4-aminobenzoyl)-glutamic acid (4-ABA-Glu), were prepared and incubated in the cecal contents. The deconjugation rates were compared with that of 5-ASA-Glu. The order of the rates was BA-Glu $approx$ 4-ABA-Glu $approx$ 3-ABA-Glu $gg$ SA-Glu $approx$ 5-ASA-Glu. The deconjugation of the aromatic acyl-L-glutamic acid derivatives was carried out by enzyme(s) in the cecal contents since the deconjugation did not occur in the autoclaved cecal contents and on incubation with N-benzoyl-D-glutamic acid. Our data suggest that the 2-hydroxyl group in 5-ASA is ascribed to the poor deconjugation of 5-ASA-Glu in the cecal contents.