Electron paramagnetic resonance (EPR) investigations were carried out on two bimetallic molecular magnets (NBu4)(2)Co-2[Cu(opba)](3) . S, where S = 3DMSO . 3H(2)O and 2H(2)O. known to exhibit long-range magnetic order below 32 and 34 K, respectively, in the temperature range 300-15 K. Temperature dependence of the intensity of the EPR signal arising from Cu2+ in these compounds showed a rapid decrease in intensity upon cooling below 65 K, which was accompanied by a disappearance of the super-hyperfine structures, observed on the Cu2+ signal at higher temperatures, pointing to a Co2+-Cu2+ spin-spin interaction following the slowing down of Co2+ spin-lattice relaxation. The appearance of a new signal at zero field (ZFS) below 40 K is attributed to the onset of long-range magnetic ordering in both the compounds. (C) 2002 Published by Elsevier Science B.V.