The pK(a) values of the succinic acid moieties of hydrolyzed alternating ethene- and isobutene-maleic anhydride copolymers were determined in D2O. The pn-dependence on the C-13 chemical shift of selected signals was analyzed for these copolymers. Four different pK(a)s were determined for the copolymer with ethene due to the existence of both the erythro- and three-configuration of the succinic acid moiety : PK01,erythro = 4.2, pK(01,threo) = 4.1, pK(02,erythro) = 6.1, pK(02,threo) = 6.8. The isobutene-maleic anhydride copolymer contains only threo-units. Therefore, only two dissociation steps with pK(01) = 3.0 and pK(02) = 8.7 were observed for the hydrolyzed form.