The quantum spin liquid (QSL) state is of great interest in relation to quantum computation and superconductivity and the search for new QSL materials is a current challenge in chemistry. Existing inorganic and molecular QSL compounds have two-dimensional structures, with spins arranged on triangular and kagome lattices, whereas three-dimensional structures with QSL characteristics are rare. In the copper-oxalate framework compound [(C2H5)(3)NH](2)Cu-2(C2O4)3, Cu(II) is coordinated with three bisbidentate oxalate bridges to form a three-dimensional (10,3) lattice and this produces a strong antiferromagnetic interaction between Cu2+(S = 1/2) atoms (theta = -180 K). No long-range ordering (LRO) was observed in either magnetic susceptibility or specific heat measurements down to 2 K. Absence of LRO was further confirmed by mu SR measurements down to 60 mK, indicating that it is a gapless QSL with f > 3000. Due to Jahn-Teller distortion and partial dimerization, the effective dimensionality of the magnetic lattice is reduced. This compound nevertheless highlights the great potential for obtaining QSLs of varying dimensionality from metal-organic frameworks.