The polycondensations of L-aspartic acid (1) with aromatic aminocarboxylic acid, 4-aminobenzoic acid (2a), 4-aminophenylacetic acid (2b), 4-aminomethylbenzoic acid (2c), 4-(4-aminophenyl)butyric acid (2d), and 4-aminocinnamic acid (2e) were carried out using phosphoric acid as a catalyst. The obtained copolymers consiting of the succinimide and amide units, poly(succinimide-co-amide) (3), were soluble in DMF and DMSO except for that with 2e. The thermal properties differed with varying the 2 unit in 3, i.e., the T(g)s of 3a-c (99 similar to 138 degrees C) were higher than those of 3d (81 similar to 1 01 degrees C), the apparent difference in the T-m between 3a-d did not observed, and the Td decreased in the order of 3a, 3c > 3d > 3b.