Copper(II) fumarate complex with 2,2' - bipyridine, [Cu-2(fum)(bipy)(4)] [fum]. 12H(2)O, has been synthesized and characterized by elemental analyses, IR, electronic reflectance spectra and magnetic studies. The single crystal X- ray diffraction study shows that the complex is triclinic, with space group P (1) over bar (#2), a=1.0697(2)nm, b=1.2820(2)nm, c=1.0470(3)nm, a=101.88(2)degrees, beta =101.93(2)degrees, gamma= 79.41(1)degrees, Z =1, and R =0. 033. Two copper( II) atoms are bridged by a fumarate group, with each copper( II) atom coordinated with two 2,2' - bipyridine molecules, forming a distorted trigonal bipyramidal configuration. The alternating temperature magnetic susceptibility study suggest that there exist weak ferromagnetic interaction between two copper( II) atoms.