A new thulium(III)-copper(I) heterometallic coordination polymer, [Cu(4)Tm(2)Br(3)(C(6)H(4)NO(2))(6)(OH)(H(2)O)(4)](n), has been prepared by a hydro-thermal method. The Tm and both Cu atoms lie on mirror planes. The Tm atom is seven-coordinate with a capped distorted trigonal-prismatic coordination geometry, while the Cu atoms adopt trigonal CuBrN(2) and tetra-hedral CuBr(3)N coordination modes, respectively. The Cu atom in the trigonal coordination environment is disordered over two sites of equal occupancy. The crystal structure is constructed from two distinct units of dimeric [Tm(2)(μ(2)-OH(IN)(6)(H(2)O)(4)] cores (IN = isonicotinate) and one-dimensional inorganic [Cu(4)Br(3)](n) chains, which are linked together, forming heterometallic Cu-halide-lanthanide-organic layers.