A process for converting molybdenum technical oxide, partially oxidized MoS.sub.2 or off-spec products from MoS.sub.2 oxidation processes into a purified molybdenum trioxide product is provided, generally comprising the steps of: combining molybdenum technical oxide with an oxidizing agent and a leaching agent in a reactor under suitable conditions to effectuate the oxidation of residual MoS.sub.2, MoO.sub.2 and other oxidizable molybdenum oxide species to MoO.sub.3, as well as the leaching of any metal oxide impurities; precipitating the MoO.sub.3 species in a suitable crystal form; filtering and drying the crystallized MoO.sub.3 product; and recovering and recycling any solubilized molybdenum.