A pneumatic studless tire comprises a tread provided with a plurality of circumferential grooves, a plurality of lateral grooves and many blocks defined by these circumferential grooves and lateral grooves, in which (1) a plurality of wave-shaped sipes are formed in each of the blocks so as to make them dense at central region of the block in the widthwise direction of the tire and sparse at both side regions thereof, and (2) an amplitude of the wave-shaped sipe in each side region of the block is smaller than that in the central region of the block.