Cyclopropane hydrogenation reaction was performed in a differential reactor operating at atmospheric pressure, 50‡C and H2/C3H6 ratio of 9, and the deactivation of the catalysts during the reaction was investigated by observing the effects of the supports and the size of platinum crystallites, Owinglo the accumulation of the carbonaceous materials the platinum catalysts dispersed on the acidic supports such as γ-Al2O3, SiO2-Al2O3 and Y-zeolite deactivated significantly, while no detectable deactivation was observed for the catalysts on the non-acidic supports of SiO2 and active carbon. In addition smaller platinum particles on acidic supports were morevulnerable to the catalyst deactivation.