Epoxidation of an olefin is carried out by continuously reacting the olefin with hydrogen peroxide in the presence of a water soluble epoxidation catalyst, comprising a manganese complex, in a reaction mixture comprising an aqueous liquid phase and an organic liquid phase using a loop reactor with mixing of the liquid phases, and during the reaction the concentration of hydrogen peroxide in the aqueous liquid phase is maintained at less than 1.0% by weight.