Two heterometallic 3dā4f coordination polymers, [Gd(CuL)2(Hbtca)(btca)(H2O)]·2H2O (1) and [Er(CuL)2(Hbtca)(btca)(H2O)]·H2O·CH3OH (2) (CuL, H2L = 2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien; H2btca = benzotriazole-5-carboxylic acid) were synthesized by solvothermal methods and characterized by single-crystal X-ray diffraction. Complexes 1 and 2 exhibit a double-strand meso-helical chain structures formed by [LnIIICuII2] (LnIII = Gd, Er) units by oxamide and benzotriazole-5-carboxylate bridges. They are isomorphic except that one free water molecule of 1 is replaced by a methanol molecule. All 1D chains are further interlinked by hydrogen bonds resulting in a 3D supramolecular architecture. The magnetic properties of the compound 1 and 2 are also discussed.