Cyclopropane hydrogenation reaction was performed in a differential reactor operating at atmospheric pressure, 50℃ 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. Owing to the accumulation of the carbonaceous materials the platinum catalysts dispersed on the acidic supports such as -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 more vulnerable to the catalyst deactivation.