We have studied the hydrogenation of cyclopentene, cyclohexene, cycloheptene, and cis-cyclooctene over Pd/alumina, Pd/carbon, Pd/silica, and Pd/zirconia catalysts. The hydrogenation reaction and the carbon deposition reaction both showed evidence for particle size sensitivity. The trend in activity with particle size was not the same for all the cycloalkenes, with cycloheptene hydrogenation increasing with particle size, whereas for the other cycloalkenes tested, the activity maximised at approximately 3.5 nm. The origin of these effects is suggested to be related to the mode and strength of adsorption of the cycloalkene.