A continuous process for preparing propylene oxide comprising a start-up stage and a normal run stage, wherein the normal run stage comprises (i) continuously providing a liquid feed stream comprising propene, hydrogen peroxide, acetonitrile, a formate salt, water and optionally propane, wherein in the liquid feed stream, the molar amount of the formate salt relative to the molar amount of hydrogen peroxide at a given point of time during the normal run stage is a N (Fo/H 2 O 2); (ii) continuously passing the liquid feed stream provided in (i) into an epoxidation zone comprising a catalyst comprising a titanium zeolite having framework type MWW, and subjecting the liquid feed stream to epoxidation reaction conditions in the epoxidation zone, obtaining a reaction mixture comprising propylene oxide, acetonitrile, water, the formate salt, optionally propene, and optionally propane; (iii) continuously removing an effluent stream from the epoxidation zone, the effluent stream comprising propylene oxide, acetonitrile, water, at least a portion of the formate salt, optionally propene, and optionally propane; wherein the normal run stage is characterized in an average rate of change of a N (Fo/H 2 O 2) of less than 0 h -1; wherein the start-up stage, which is prior to the normal run stage, comprises (a) continuously providing a liquid feed stream comprising propene, acetonitrile, and optionally propane and continuously passing said liquid feed stream under start-up conditions for a period of time t 1 into the epoxidation zone comprising the catalyst comprising a titanium zeolite having framework type MWW; wherein after the period of time t 1, the start-up stage further comprises (b) continuously providing a liquid feed stream comprising hydrogen peroxide, admixing said liquid feed stream to the liquid feed stream provided in (a) obtaining a liquid feed stream comprising hydrogen peroxide, propene, acetonitrile, and optionally propane, and continuously passing said liquid feed stream under start-up conditions for a period of time t 2 into the epoxidation zone comprising the catalyst comprising a titanium zeolite having framework structure type MWW, wherein the liquid feed stream according to (b) comprises the formate salt, wherein the molar amount of the formate salt relative to the molar amount of hydrogen peroxide at a given point of time during step (b) of the start-up stage is a S (Fo/H 2 O 2), wherein after the period of time t 2, the normal run stage begins and a S (Fo/H 2 O 2) is a N (Fo/H 2 O 2) at the beginning of the normal run stage. (i) continuously providing a liquid feed stream comprising propene, hydrogen peroxide, acetonitrile, a formate salt, water and optionally propane, wherein in the liquid feed stream, the molar amount of the formate salt relative to the molar amount of hydrogen peroxide at a given point of time during the normal run stage is a N (Fo/H 2 O 2); (ii) continuously passing the liquid feed stream provided in (i) into an epoxidation zone comprising a catalyst comprising a titanium zeolite having framework type MWW, and subjecting the liquid feed stream to epoxidation reaction conditions in the epoxidation zone, obtaining a reaction mixture comprising propylene oxide, acetonitrile, water, the formate salt, optionally propene, and optionally propane; (iii) continuously removing an effluent stream from the epoxidation zone, the effluent stream comprising propylene oxide, acetonitrile, water, at least a portion of the formate salt, optionally propene, and optionally propane; (a) continuously providing a liquid feed stream comprising propene, acetonitrile, and optionally propane and continuously passing said liquid feed stream under start-up conditions for a period of time t 1 into the epoxidation zone comprising the catalyst comprising a titanium zeolite having framework type MWW; wherein after the period of time t 1, the start-up stage further comprises (b) continuously providing a liquid feed stream comprising hydrogen peroxide, admixing said liquid feed stream to the liquid feed stream provided in (a) obtaining a liquid feed stream comprising hydrogen peroxide, propene, acetonitrile, and optionally propane, and continuously passing said liquid feed stream under start-up conditions for a period of time t 2 into the epoxidation zone comprising the catalyst comprising a titanium zeolite having framework structure type MWW,