A new 3D supramolecular complex, namely dimethylammonium 4,4΄-([2,2΄-bipyrimidine]-5,5΄-diyl)bis(2-hydroxybenzoate) dihydrate, has been synthesized by the reaction of 4,4΄-([2,2΄-bipyrimidine]-5,5΄-diyl)bis(2-hydroxybenzoic acid) with aqueous dimethylamine solution and characterized by single-crystal X-ray diffraction, ¹H NMR spectroscopy and elemental analysis. It belongs to triclinic system, space groupP with a = 6.5539(4), b = 9.4977(6), c = 12.1407(8) Å, α = 72.299(6), β = 89.160(5),  γ = 70.797(8)°, V = 676.52(8) ų, Z = 1, M_r = 556.57, µ = 0.103 mm^-1, D_c = 1.366 g/cm³, F(000) = 294, the final R =0.0828 and wR = 0.2083 for 1934 observed reflections with I > 2σ(I). The 4,4΄-([2,2΄-bipyrimidine]-5,5΄-diyl)bis(2-hydroxybenzoic acid) dianion,  dimethylammonium cation, and water molecule are interconnected by O−H∙∙∙O, N−H∙∙∙N, and N−H∙∙∙O  hydrogen bonds, forming a two-dimensional (2D) layer. Two adjacent2D layers are further stacked into a three-dimensional  supramolecular structure through O−H∙∙∙O hydrogenbonds. In addition, the luminescent property of this supramolecular complex has also been investigated.