The size effect of Pt particles on selective oxidation of glycerol to lactic acid was investigated over 1.0 wt% Pt/activated carbon catalysts in base solutions. A series of Pt/activated carbon catalysts with Pt particle size ranging from 10.2 to 3.8 nm were prepared by simply verifying the deposition-precipitation temperature from 0 to 80 A degrees C, which were characterized by XRD, CO pulse chemisorption, H-2-O-2 titration, TEM and zeta potential analyses. The Pt particle size showed evident impact on the pseudo turnover frequency of the catalyst, with the optimal activity achieved over medium-sized Pt particles. The lactic acid selectivity was less obviously affected by the Pt particle size. Meanwhile, the Pt particle size effect would be altered when factors including base type changed.