Several S-containing organic compounds were used as ligands for Cu(I)-catalyzed acetylene hydration under mercury free condition. The results show that the minimum selectivity for acetaldehyde is significantly improved from 3.61 to 87.56%, while the minimum conversion of C2H2 is also enhanced from 14.45 to 34.92%, owing to the addition of mercaptosuccinic acid. The possible reasons for the improvement in acetaldehyde selectivity were studied by the density functional theory calculations. The results show that the addition of S-containing organic compounds improves the coordinating ability of Cu complex I with C2H2. [GRAPHICS] .