Provided is a boot for a constant velocity universal joint capable of being properly engaged with an outer joint member of a constant velocity universal joint and capable of increasing durability thereof. Over a shoulder portion (5) and a root portion (13) of a boot (1) for a constant velocity universal joint according to the present invention, there are formed a circular arc portion (14) adjacent to a large diameter portion (2) and having an axial sectional shape protruding radially outward and a linear portion (15) adjacent to the circular arc portion (14) and having a linear axial sectional shape. An innerperipheral surface (16) of the linear portion (15) is brought into contact with an opening end portion (17) of an outer joint member (7) of a constant velocity universal joint (6) such that a thickness from the circular arc portion (14) to the linear portion (15) is uniform.