A boot for a universal joint capable of effectively preventing the top parts (111) of a bellows part (11) from being inverted without increasing the outer diameter of the bellows part (11) when a rotating shaft (23) is angularly displaced. The boot comprises the bellows part (11) having top parts and bottom parts repeatedly so formed as to extend in the circumferential direction, a large diameter mounting part (12) formed at one end of the bellows part and fitted to the outer peripheral surface of the outer ring (21) of the universal joint (2), and a small diameter mounting part (13) formed at the other end of the bellows part (11) and fitted to the outer peripheral surface of a rotating shaft (23) so connected to a bearing mechanism in the outer ring (21) as to be capable of free angular displacement. The first top part (111) nearest the large diameter mounting part (12) of the bellows part (11) is raised from the large diameter mounting part (12). A length (L1) between a ridge section (111a) and a foot section (111b) on the large diameter mounting part (12) side in the first top part (111) is equal to or less than a length (L2) between the inner peripheral position of the foot section (111b) and the end part (21b) of the outer ring (21) on the rotating shaft (23) side. The first bottom part (112) adjacent to the first top part (111) is positioned on the rotating shaft (23) side of the end part (21b) of the outer ring (21).