The selective hydrogenation of trans-4-phenyl-3-butene-2-one over Ru/gamma-Al2O3 stabilized with triphenylphosphine was investigated in the presence of diamine and base. It was found that 1,2-diphenylethylene-1,2-diamine (DPEN) was the best modifier among the investigated diamines. Both DPEN and KOH not only promoted the selectivity of the C=O bond hydrogenation, but also accelerated the rate of the hydrogenation. Under the optimum conditions: the reaction temperature of 35 degrees C, H-2 pressure of 4.0 MPa, KOH concentration of 0.04 mol/l, and reaction time of 3 h, the conversion of trans-4-phenyl-3-butene-2-one was close to 100% and the selectivity to unsaturated alcohol was more than 99%. In combining with the effect of reaction factors on the hydrogenation, a possible hydrogenation mechanism is proposed. (c) 2008 Elsevier B.V. All rights reserved.