A plunging type constant velocity universal joint for a rear-wheel drive shaft, comprising: an outer joint member having a cylindrical inner peripheral surface in which eight track grooves extending in an axial direction of the plunging type constant velocity universal joint are formed; an inner joint member having a spherical outer peripheral surface in which eight track grooves extending in the axial direction are formed, and having a spline hole formed along an axial center of the inner joint member; eight balls arranged in ball tracks formed by the track grooves of the outer joint member and the track grooves of the inner joint member; and a cage, which has eight pockets configured to receive the balls, and is held in slide contact with the inner peripheral surface of the outer joint member and the outer peripheral surface of the inner joint member, wherein a curvature center of a spherical portion formed on an outer peripheral surface of the cage and a curvature center of a spherical portion formed on an inner peripheral surface of the cage are offset to opposite sides in the axial direction with respect to a joint center (O(s)) by an equal distance, characterized in that the plunging type constant velocity universal joint has a maximum operating angle of 20° or less, a ratio PCD BALL /D BALL of a pitch circle diameter PCD BALL of the balls to a diameter D BALL of each of the balls is set from 3.3 to 3.6, a ratio T I /D BALL of a radial thickness T I of the inner joint member to the diameter D BALL of each of the balls is set from 0.30 to 0.45, a ratio PCD SPL /D BALL of a pitch circle diameter PCD SPL of the spline hole of the inner joint member to the diameter D BALL of each of the balls is set from 1.70 to 1.85, and a ratio W I /D BALL of an axial width W I of the inner joint member to the diameter D BALL of each of the balls is set from 1.2 to 1.55. an outer joint member having a cylindrical inner peripheral surface in which eight track grooves extending in an axial direction of the plunging type constant velocity universal joint are formed; an inner joint member having a spherical outer peripheral surface in which eight track grooves extending in the axial direction are formed, and having a spline hole formed along an axial center of the inner joint member; eight balls arranged in ball tracks formed by the track grooves of the outer joint member and the track grooves of the inner joint member; and a cage, which has eight pockets configured to receive the balls, and is held in slide contact with the inner peripheral surface of the outer joint member and the outer peripheral surface of the inner joint member, wherein a curvature center of a spherical portion formed on an outer peripheral surface of the cage and a curvature center of a spherical portion formed on an inner peripheral surface of the cage are offset to opposite sides in the axial direction with respect to a joint center (O(s)) by an equal distance, characterized in that the plunging type constant velocity universal joint has a maximum operating angle of 20° or less, a ratio PCD BALL /D BALL of a pitch circle diameter PCD BALL of the balls to a diameter D BALL of each of the balls is set from 3.3 to 3.6, a ratio T I /D BALL of a radial thickness T I of the inner joint member to the diameter D BALL of each of the balls is set from 0.30 to 0.45, a ratio PCD SPL /D BALL of a pitch circle diameter PCD SPL of the spline hole of the inner joint member to the diameter D BALL of each of the balls is set from 1.70 to 1.85, and a ratio W I /D BALL of an axial width W I of the inner joint member to the diameter D BALL of each of the balls is set from 1.2 to 1.55.