Process for preparing propylene oxide, which comprises at least the steps (i) and (ii): (i) providing a catalyst comprising at least one porous oxidic material; (ii) reacting propene with a hydroperoxide in at least one nitrile as solvent or in a solvent mixture comprising at least one nitrile in the presence of the catalyst of (i), wherein the at least one porous oxidic material is a zeolite which is assigned X-ray-crystallographically to the MWW type.