Infrared (IR) and ultraviolet (UV) absorption spectra of poly(fumaric acid) (PFA) and its stereoisomer, poly(maleic acid) (PMA), in aqueous solution at various degree of neutralization (a) were measured to study their dissociation behavior and to compare with those of an alternating copolymer of isobutylene and maleic acid (PIM), whose carboxyl groups show a definite intramolecular ionic hydrogen bonding between nearest-neighbor carboxyl groups during neutralization as reported in the previous paper. In UV spectra, the absorbance of PFA and PMA in the vicinity of lambda = 220 nm was found to increase with a up to a = 0.6 and then decrease with a. The IR spectra of PFA and PMA revealed that, above a = 0.5, a stretching vibration band of C = O of COOH shifts to lower wavenumbers by about 25 cm-1 and an asymmetric stretching vibration band of COO also shifts to lower wavenumbers by about 24 cm-1. The IR bands ascribed to carboxyl groups of PFA were resolved into those of four species, that is, free COOH, free COO-, hydrogen-bonded COOH, and hydrogen-bonded COO-. It was shown that PFA has both free and hydrogen-bonded COO- as well as both free and hydrogen-bonded COOH at a = 0.5. The IR bands of PMA, however, could not be resolved by those only four species over a whole a. It appears that PMA has the hydrogen bonding formed over four adjacent COOH's which can resonate each other. The difference in the dissociation process between PFA and PMA was discussed from a viewpoint of their configurational difference. The most probable dissociation process for PFA and PMA was proposed and discussed in view of the results of potentiometric titration.