In a locking structure of a cable tie, the cable tie includes a strap portion and a head portion. A first locking hole at a proximal end of the strap portion, and a second locking hole of the head portion, are formed in a shape wherein their widths in a short-side direction of the strap portion are longer than those in a longitudinal direction of the strap portion, and include a first inner wall surface and a second inner wall surface, respectively, that extend in a direction substantially orthogonal to the longitudinal direction of the strap portion, on the side nearer to the proximal end of the cable tie. The distal end of the strap portion has a protruded portion that protrudes through the first locking hole and into the second locking hole.