The hydrogenation of ethyne on a gamma-Mo2N catalyst has been investigated at 50-210 degrees C. With reaction time increasing, the selectivity of ethene in the products rose up gradually at 150 degrees C. A conversion of ca. 85% ethyne and selectivity of ca. 85% for ethene were obtained at 130 degrees C after the reaction became steady. Selectivity remained almost unchanged with the varying of reaction temperature and space velocity. These results can be explained by Bond's model, and firmly held adspecies (FHA) and/or coke species from ethyne may be responsible for the high selectivity of ethene.