A Cu(II)-Gd(III) heteronuclear complex with N,N′-ethylene-bis-5-methoxy salicylaldiimine (ems) as ligand has been synthesized. The complex crystallizes in the monoclinic system C2/c space group. The structure consists of two different discrete molecules: a mononuclear unit containing a single Cu(II) center, and a dinuclear one containing both a nine coordinated Gd(III) plus a four coordinated Cu(II) cation [CuGd(H₂O)(NO₃)(ems)]. The complex was characterized by magnetic susceptibility and electron paramagnetic resonance. The Cu(II)-Gd(III) complex presents a ferromagnetic interaction (J=1.88 cm^-1); its effective magnetic moment was found to increase with decreasing temperature. Both electronic and structural parameters are shown to influence the magnitude of the magnetic interaction.