A bicycle axle, including: a mandrel, defining an axial direction, including an axial rod and a head portion radially protruding from an end of the axial rod; a sleeve member, being sleeved around the head portion, including a flange radially extending inwardly; wherein the axial rod has an engaging portion radially disposed thereon, the engaging portion and the flange are overlapped with the head portion in the axial direction, and the sleeve member is rotatably restricted to the head portion by the engaging portion, wherein the engaging portion radially protrudes from the axial rod and is axially spaced apart from the head portion, wherein at least a part of the flange is located between the head portion and the engaging portion and is abuttable against the head portion and the engaging portion in the axial direction, wherein an inner circumferential surface of the flange has a lip radially and inwardly protruding therefrom, wherein the lip is located between the head portion and the engaging portion and is interferable with the head portion and the engaging portion in the axial direction, wherein the engaging portion includes at least one engaging projection, at least a part of the flange being interferable with the at least one engaging projection in the axial direction, the at least one engaging projection being an annular projection disposed on the axial rod, wherein the flange defines a penetrating hole through which the mandrel penetrates, in the axial direction, a distance between the head portion and the engaging portion is larger than or equal to a thickness of the lip, and relative to an axle center of the axial rod, a minimum diametric dimension of the penetrating hole is smaller than a maximum diametric dimension of the engaging portion, wherein an end of the axial rod opposite to the head portion has a threaded segment, characterized in that the annular projection includes an inclined guiding surface located at a side remote from the head portion, wherein each of two end surfaces of the axial rod has an assembling hole. a mandrel, defining an axial direction, including an axial rod and a head portion radially protruding from an end of the axial rod; a sleeve member, being sleeved around the head portion, including a flange radially extending inwardly; wherein the axial rod has an engaging portion radially disposed thereon, the engaging portion and the flange are overlapped with the head portion in the axial direction, and the sleeve member is rotatably restricted to the head portion by the engaging portion, wherein the engaging portion radially protrudes from the axial rod and is axially spaced apart from the head portion, wherein at least a part of the flange is located between the head portion and the engaging portion and is abuttable against the head portion and the engaging portion in the axial direction, wherein an inner circumferential surface of the flange has a lip radially and inwardly protruding therefrom, wherein the lip is located between the head portion and the engaging portion and is interferable with the head portion and the engaging portion in the axial direction, wherein the engaging portion includes at least one engaging projection, at least a part of the flange being interferable with the at least one engaging projection in the axial direction, the at least one engaging projection being an annular projection disposed on the axial rod, wherein the flange defines a penetrating hole through which the mandrel penetrates, in the axial direction, a distance between the head portion and the engaging portion is larger than or equal to a thickness of the lip, and relative to an axle center of the axial rod, a minimum diametric dimension of the penetrating hole is smaller than a maximum diametric dimension of the engaging portion, wherein an end of the axial rod opposite to the head portion has a threaded segment, characterized in that the annular projection includes an inclined guiding surface located at a side remote from the head portion, wherein each of two end surfaces of the axial rod has an assembling hole.