Disclosed herein is a kerf of a winter tire capable of easily discharging snow therefrom and further improving braking performance and drainage performance on a wet road. The kerf includes a kerf inlet portion formed in the shape of a sawtooth-type zigzag wave in a block of one of a tread and a shoulder of the tire in the circumferential direction of the tire, a pipe-shaped flow passage portion formed in a lower portion of the block and having a width that is greater than or equal to the width of the kerf inlet portion, and a connection channel for connecting the kerf inlet portion and the flow passage portion to each other. The sawtooth-type zigzag wave has an amplitude that gradually decreases in the depth direction of the block, and the connection channel has a width that gradually decreases from the kerf inlet portion to the flow passage portion.