Vapor-phase epoxidation of propylene to propylene oxide (PO) using H-2 and O-2 has been carried out over Au deposited on Ti-MCM-41 and TiO2-SiO2 mixed oxides having various Ti/Si molar ratios ranging from 0.25/100 to 6.0/100. The Ti-MCM-41 supports were prepared by using two different structure-directing organic templates: dodecyltrimethylammonium hydroxide (C12TMACl) and cetyltrimethylammonium hydroxide (C16TMACl). TiO2-SiO2 mixed oxides were prepared by a sol-gel process. Gold nano-particles were loaded by deposition-precipitation (DP) using various precipitating agents: LiOH, NaOH, KOH, RbOH, and CsOH. Au/Ti-MCM-41 gives increased propylene conversion with an increase in Ti/Si ratio and the PO yield passes through a maximum (conversion = 3.2%, PO selectivity = 93.5%) at 100 degreesC at a Ti/Si molar ratio of 3/100. However, at higher reaction temperatures of greater than or equal to 120 degreesC, PO selectivity decreases with an increase in the Ti/Si ratio. At the reaction temperatures of 150 and 200 degreesC, to get better performance, the ideal catalysts should have Ti/Si ratios of 2/100 and 1.5/100, respectively. The critical balance among Ti-content, Au loading and the reaction temperature is important to achieve the higher propylene conversion, PO selectivity above 90% and lower H-2 (and O-2) consumption. Gold supported on TiO2-SiO2 mixed oxides showed very poor performance, probably due to higher concentrations of extra framework titanium and lower dispersion of gold particles.