A blow-by gas filtration assembly which is fluidly connectable to the crankcase ventilation circuit of an internal combustion engine to receive blow-by gases and filter from them the suspended particles contained therein, wherein the filtration assembly has an axis (X-X) and comprises: - a support body comprising a filtration chamber extending along said axis (X-X), an inlet mouth of the blow-by gases to be filtered and an outlet mouth of the filtered blow-by gases, wherein the outlet mouth of the filtered blow-by gases is preferably positioned radially spaced apart from the axis (X-X); - a filter group which extends along the axis (X-X) and has a hollow cylindrical shape having a central cavity which can be crossed radially by the blow-by gases from the outside to the inside; - a control drive operatively connected to the filter group to command it in rotation about the axis (X-X) and to perform the filtration operations; - a shaft, for support and control, extending along the axis (X-X) defining internally an air duct through which the filtered blow-by gases flow, wherein the shaft comprises: i) a filter portion on which the filter group is mounted; ii) a control portion operatively connected to the control drive; iii) an outflow portion axially positioned between the filter portion and the control portion, wherein said outflow portion comprises at least one outflow window through which the filtered blow-by gases flow towards the outlet mouth; wherein the blow-by gas filtration assembly is characterized by the fact that the support body comprises a main body and an auxiliary body mutually sealingly engageable along the axis (X-X) so as to hermetically delimit the filtration chamber, wherein the main body and the auxiliary body in the reciprocal coupling delimit an outflow chamber fluidically connected to the outflow portion of the shaft and to the outlet mouth of the blow-by gases. - a support body comprising a filtration chamber extending along said axis (X-X), an inlet mouth of the blow-by gases to be filtered and an outlet mouth of the filtered blow-by gases, wherein the outlet mouth of the filtered blow-by gases is preferably positioned radially spaced apart from the axis (X-X); - a filter group which extends along the axis (X-X) and has a hollow cylindrical shape having a central cavity which can be crossed radially by the blow-by gases from the outside to the inside; - a control drive operatively connected to the filter group to command it in rotation about the axis (X-X) and to perform the filtration operations; - a shaft, for support and control, extending along the axis (X-X) defining internally an air duct through which the filtered blow-by gases flow, wherein the shaft comprises: i) a filter portion on which the filter group is mounted; ii) a control portion operatively connected to the control drive; iii) an outflow portion axially positioned between the filter portion and the control portion, wherein said outflow portion comprises at least one outflow window through which the filtered blow-by gases flow towards the outlet mouth; i) a filter portion on which the filter group is mounted; ii) a control portion operatively connected to the control drive; iii) an outflow portion axially positioned between the filter portion and the control portion, wherein said outflow portion comprises at least one outflow window through which the filtered blow-by gases flow towards the outlet mouth;