In supercritical carbon dioxide medium, a platinum-containing cubic mesoporous molecular sieve was shown to promote markedly the selective hydrogenation of trans-cinnamaldehyde, giving an excellent selectivity for cinnamyl alcohol. In contrast to the other platinum-containing conventional catalysts, Pt-MCM-48 can be recycled a number of times without showing any deactivation in the studied reaction condition. The selectivity mainly depends on the pressure of carbon dioxide, while the conversion depends on the pressure of carbon dioxide as well as hydrogen pressure.