A process of activating a fresh catalyst or regenerating a deactivated catalyst which is used in a hydro-oxidation process, preferably, the hydro-oxidation of an olefin in the presence of oxygen and hydrogen to an olefin oxide. The hydro-oxidation catalyst preferably comprises at least one metal selected from gold, silver, the platinum group metals, the lanthanide metals, and combinations thereof, incorporated onto a titanium- , vanadium- , or zirconium-containing support, more preferably, a titanium-containing support, such as titanium oxide or a titanosilicate. The activation or regeneration process involves contacting the fresh catalyst or the deactivated catalyst with ozone.