A novel Nieuwland catalytic system, containing 5 mol% of 4-hydrazinylbenzenesulfonic acid (S-8), was developed and exhibited an excellent catalytic performance and good stability in the acetylene dimerization reaction. The acetylene conversion reached 57.1%, while the selectivity of monovinylacetylene (MVA) was 75.1%. The yield of MVA was maintained at 42.9% under an acetylene gas hourly space velocity (GHSV) of 80 h(-1) at 80 degrees C, which was increased by 18.8% over the control Nieuwland catalytic system. The addition of S-8 increased the dissolution of CuCl in water, inhibited the polymer formation, and hindered the Cu+ loss during the reaction process, thus improving the activity and the long-term stability of the modified Nieuwland catalyst.