In order to establish a strategy for minimizing Pt usage in catalysts for aqueous-phase reforming of glycerol, we studied turnover frequency (TOP) using a series of Pt/Al2O3 catalysts with different mean Pt diameters. It was found that TOP increases with decreasing Pt diameter, and the increase is drastically enhanced below a threshold diameter. This suggests that Pt utilization rapidly increases across the threshold because of the combined effect of the increase in the specific surface area and TOP of Pt.