In the crystal structure of the title complex, [Tb(C(6)H(4)NO(2))(C(2)O(4))(H(2)O)(2)](n), the Tb(III) ion is coordinated by two O atoms from two isonicotinate (inic) anions, four O atoms of two oxalate anions, and two water mol-ecules, displaying a distorted square-antiprismatic geometry. The Tb(III) ion, the inic anion and the water mol-ecules occupy general positions. One of the two crystallographically independent oxalate anions is located on a center of inversion, whereas the second is located on the twofold rotation axis. The carboxyl-ate groups of the inic and oxalate anions link the terbium metal centres into layers. These layers are connected by O-H⋯O and N-H⋯O hydrogen bonding into a three-dimensional network.