Cu-Mo composites have been one of candidates for material of heat-sinks in electronic devices. We obtained Cu-Mo composites by electrodeposition using CuSO4 and Na2MoO4 with trisodium citrate as complexing agent. The presence of molybdenum in Cu-Mo was demonstrated by X-ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy. The molybdenum content inCu-Mo composites depended on the concentration ratio of Na2MoO4/(Na2MoO4 + CuSO4) in the electrolyte, kinds and concentration of complexing agents. The mol ratio of Na2MoO4/(Na2MoO4 + CuSO4), from 0.75 to 0.87 provided larger molybdenum content at 0.05 A/dm(2) of electrodeposition current. The molybdenum content increased with decreasing current density during electrodeposition in the range of 0.05-0.3 A/dm(2). Trisodium citrate was the most effective complexing agent among trisodium citrate, glycolic acid, EDTA (4Na) and combinations of them for increasing molybdenum content. The molybdenum content reached up to 22.9 wt% at 0.396 mol/dm(3) of trisodium citrate concentration. X-ray diffraction shows that no peaks related to molybdenum was observed, moreover, the intensity and the width of Cu(111) peaks decreased and enlarged with increasing molybdenum content. These indicate that the structure of molybdenum in copper-molybdenum composites was amorphous, furthermore, higher molybdenum content made copper structure close to amorphous. (c) 2014 The Electrochemical Society. All rights reserved.