The vapour phase hydrogenation of cinnamaldehyde over Ni loading gamma-Al2O3 catalysts was performed at 1 atm and 300 degrees C in a fixed-bed reactor. The major product was hydrocinnamaldehyde. Unexpected products of styrene and ethylbenzene due to new reaction pathway of hydrodeformylation were observed. The results indicated that Ni metal was the active centers and the catalytic activity was parallel to the Ni surface area. The stability of TOF values implied that the cinnamaldehyde hydrogenation over Ni/gamma-Al2O3 catalysts was a structure insensitive reaction.