A fan rotor blade for an aircraft jet engine configured to be held by a fan disk and to take external air into a passage formed in an engine case by rotating integrally with the fan disk, the fan rotor blade comprising: a blade body made from a composite material of a resin and reinforcing fibers, including a pressure surface facing one side in a thickness direction and a suction surface facing the other side in the thickness direction, and one end side of the blade body in a longitudinal direction being held by the fan disk; and a sheath being more rigid than the blade body, extending in the longitudinal direction of the blade body from one end side to the other end side in the longitudinal direction of the blade body, and fixed to the blade body so that the sheath covers a leading edge portion of the blade body and the vicinity thereof, the leading edge portion being located on an upstream side in a direction of intake of the external air; wherein a tip end portion of the sheath, which covers the other end side of the blade body in the longitudinal direction, extends from the leading edge portion side of the blade body to a trailing edge portion side of the blade body located in a downstream side in the direction of intake of the external air, and characterized in that an end portion (x) of the tip end portion of the sheath on the downstream side in the direction of intake of the external air either (a) is located closer than the trailing edge portion of blade body to a leading edge side of the fan rotor blade and is located no more than 20% of the chord length of the fan rotor blade from its trailing edge; or (b) projects from the trailing edge portion of the blade body toward the downstream side in the direction of the intake of the external air. a blade body made from a composite material of a resin and reinforcing fibers, including a pressure surface facing one side in a thickness direction and a suction surface facing the other side in the thickness direction, and one end side of the blade body in a longitudinal direction being held by the fan disk; and a sheath being more rigid than the blade body, extending in the longitudinal direction of the blade body from one end side to the other end side in the longitudinal direction of the blade body, and fixed to the blade body so that the sheath covers a leading edge portion of the blade body and the vicinity thereof, the leading edge portion being located on an upstream side in a direction of intake of the external air; wherein a tip end portion of the sheath, which covers the other end side of the blade body in the longitudinal direction, extends from the leading edge portion side of the blade body to a trailing edge portion side of the blade body located in a downstream side in the direction of intake of the external air, and characterized in that an end portion (x) of the tip end portion of the sheath on the downstream side in the direction of intake of the external air either (a) is located closer than the trailing edge portion of blade body to a leading edge side of the fan rotor blade and is located no more than 20% of the chord length of the fan rotor blade from its trailing edge; or (b) projects from the trailing edge portion of the blade body toward the downstream side in the direction of the intake of the external air.