In the title compound, {[AgSm(C(6)H(4)NO(2))(2)(C(2)O(4))]·H(2)O}(n), the asymmetric unit contains one Sm(III) ion, one Ag(I) ion, two unique isonicotinate (ina) ligands, two half oxalate (ox) ligands (one on an inversion centre, the other on a twofold axis) and one uncoordinated water mol-ecule. The central Sm(III) ion is nine-coordinated by four O-donor atoms from separate bidentate bridging ox ligands and five O-donor atoms from the two ina ligands (both bidentate) and a symmetry-related ina ligand [Sm-O = 2.389 (4)-2.791 (4) Å], giving a distorted monocapped square anti-prismatic geometry. The Ag(I) ion is three-coordinated in a T-shaped geometry involving two ina N-donor atoms [Ag-N = 2.181 (6) and 2.185 (5) Å] and a bridging oxalate O-donor atom [Ag-O = 2.620 (4) Å]. The three-dimensional heterometallic Sm-Ag coordination polymer, having a unique (3,4,6)-connected five-nodal net topology, is constructed from two-dimensional samarium-oxalate layers and pillared Ag(ina)(2) subunits. Inter-molecular water-carboxyl-ate O-H⋯O hydrogen-bonding inter-actions are also present.