A process for the manufacture of propylene oxide (“PO”) by catalytic oxidation of propylene with an oxidant wherein the catalytic oxidation is performed in an aqueous reaction medium, comprising water with less than 10% by volume of cosolvents, wherein a water-soluble manganese complex is used as oxidation catalyst,characterized in that the water-soluble manganese complex is a mononuclear species of the general formula (I): [LMnX3]Y   (I) or a binuclear species of the general formula (II): [LMn(μ-X)3MnL]Y2   (II) wherein Mn is a manganese; L or each L independently is a polydentate ligand, each X independently is a coordinating species and each μ-X independently is a bridging coordinating species, whereas Y is an non-coordinating counterion, and wherein the catalytic oxidation is carried out at a pH in the range of from 1.5 to 6.0.