Process to make ethylene and propylene, in a combined XTO-OC process, from an oxygen-containing organic feedstock being methanol, dimethyl ether, or a mixture thereof comprising: a) providing a catalyst comprising zeolitic molecular sieves containing 10 membered rings pore opening in their microporous structure, b) providing an XTO reaction zone using a fluidized bed reactor, an OC reaction zone using a fluidized bed and a catalyst regeneration zone using a fast fluidized bed system, said catalyst circulating in the three zones, such that at least a portion of the regenerated catalyst is passed to the OC reaction zone, at least a portion of the catalyst in the OC reaction zone is passed to the XTO reaction zone and at least a portion of the catalyst in the XTO reaction zone is passed to the regeneration zone; c) contacting said oxygen-containing organic feedstock in the XTO reactor with the catalyst at conditions effective to convert at least a portion of the feedstock to form a XTO reactor effluent comprising ethylene and propylene and a hydrocarbon fraction containing C4-C7 olefins; d) separating said ethylene and propylene from said hydrocarbon fraction containing C4-C7 olefins; e) contacting said hydrocarbon fraction containing C4-C7 olefins in the OC reactor with the catalyst at an inlet temperature of 400 to 650°C. a LHSV ranging from 0.5 to 30 hr -1. an olefin partial pressure of 10kPa to 200kPa (0.1 to 2 bars) to convert at least a portion of said hydrocarbon fraction containing C4-C7 olefins to ethylene and propylene, wherein the paraffin's content in the feed at the inlet in OC reactor is at least 20 wt% on carbon basis and wherein said zeolitic molecular sieve provided in a) is an alkaline earth or rare earth metal P-modified molecular sieve, M-P-modified molecular sieve wherein the P-content in the M-P-modified molecular sieve is at least 0.3 wt%, the amount of alkaline earth or rare earth metal in the M-P-modified molecular sieve is at least 0.05 wt%, the molar ratio of M/P in the M-P-modified molecular sieve is less than 1, wherein the M-P-modified molecular sieve made by a process comprising the following steps: a). selecting a P-modified molecular sieve which contains at least 0.3 wt% of P wherein the molecular sieve is an aluminosilicate of the MFI structure: b). contacting the P-modified molecular sieve selected in a) with a solution of an alkaline earth or rare earth metal-containing compound, M-containing compound, to introduce at least 0.05 wt% of the alkaline earth or rare earth metal M and wherein the process further comprises the following steps, in the order given: - separation of the solid from the liquid; - an optional washing step or an optional drying step followed by a washing step: - a calcination step. a) providing a catalyst comprising zeolitic molecular sieves containing 10 membered rings pore opening in their microporous structure, b) providing an XTO reaction zone using a fluidized bed reactor, an OC reaction zone using a fluidized bed and a catalyst regeneration zone using a fast fluidized bed system, said catalyst circulating in the three zones, such that at least a portion of the regenerated catalyst is passed to the OC reaction zone, at least a portion of the catalyst in the OC reaction zone is passed to the XTO reaction zone and at least a portion of the catalyst in the XTO reaction zone is passed to the regeneration zone; c) contacting said oxygen-containing organic feedstock in the XTO reactor with the catalyst at conditions effective to convert at least a portion of the feedstock to form a XTO reactor effluent comprising ethylene and propylene and a hydrocarbon fraction containing C4-C7 olefins; d) separating said ethylene and propylene from said hydrocarbon fraction containing C4-C7 olefins; e) contacting said hydrocarbon fraction containing C4-C7 olefins in the OC reactor with the catalyst at an inlet temperature of 400 to 650°C. a LHSV ranging from 0.5 to 30 hr -1. an olefin partial pressure of 10kPa to 200kPa (0.1 to 2 bars) to convert at least a portion of said hydrocarbon fraction containing C4-C7 olefins to ethylene and propylene, wherein the paraffin's content in the feed at the inlet in OC reactor is at least 20 wt% on carbon basis and wherein said zeolitic molecular sieve provided in a) is an alkaline earth or rare earth metal P-modified molecular sieve, M-P-modified molecular sieve a). selecting a P-modified molecular sieve which contains at least 0.3 wt% of P wherein the molecular sieve is an aluminosilicate of the MFI structure: b). contacting the P-modified molecular sieve selected in a) with a solution of an alkaline earth or rare earth metal-containing compound, M-containing compound, to introduce at least 0.05 wt% of the alkaline earth or rare earth metal M and wherein the process further comprises the following steps, in the order given: - separation of the solid from the liquid; - an optional washing step or an optional drying step followed by a washing step: - a calcination step. - separation of the solid from the liquid; - an optional washing step or an optional drying step followed by a washing step: - a calcination step.