Evidence of the catalysed decomposition of N2H4 and its salts by a Y-Ba-Cu-O superconductor is presented. A thermostated aqueous suspension of the superconductor, treated with a solution of N2H5+Cl-, produced nitrogen and hydrogen gases, whose volumes were measured at intervals in a gas burette. Two simultaneous reactions are suggested for the reaction between the N2H5+ solution and Y-Ba-Cu-O. One is the reduction of Cu3+ ions in Y-Ba-Cu-O to Cu2+ producing nitrogen, and the other is the catalysed decomposition of N2H5+ by Cu2+ ions in Y-Ba-Cu-O, producing nitrogen and hydrogen. The rates of hydrogen evolution at different initial concentrations of N2H5+ are given. First-order kinetics at the initial stages of the N2H5+/Y-Ba-Cu-O reaction were obtained. A comparison between the total nitrogen and hydrogen gases liberated from the reaction shows that the reduction reaction goes faster than the catalysed one. The rate of the catalysed reaction is increased as the initial concentration of the N2H5+ solution increases.