Selective hydrogenation of C5 hydrocarbons from steam cracker was studied. Experiments were carried out in a fixed-bed reactor at 40 degrees C-80 degrees C and 0.3-2.5 MPa over a commercial nickel-alumina catalyst. The results show that the conversion of diolefins and selectivity of mono-olefins increase as temperature increases, but when the temperature is above 60 degrees C, the selectivity of mono-olefins decreases. With the increasing reaction pressure and the molar ratio of hydrogen and olefins, the loss of the mono-olefins increases, whereas the selectivity of mono-olefins increases as the liquid hourly space velocity (LHSV) increases. The optimal conditions are: pressure 0.5-1.0, temperature 50 degrees C-60 degrees C, LHSV 1.0-2.0 h(-1), molar ratio of hydrogen and olefins 1.0-1.2. The stability testing illustrated the catalyst's high stability and activity; it is a fine commercial catalyst for selective hydrogenation.