A pet leash has an extended leash section, in an extended leash body form, with a pulling and holding end and an extended end. A scalable adjustment ring is connected to the extended end of the extended leash section, A C-shaped collar is connected to the scalable adjustment ring. The two opposite ends of the C-shaped collar are provided with two buckles to be connected to the adjustment ring. The two buckles can move along the shape of the adjustment ring to change the diameter of the collar. Thus, through adjusting the diameter size of the scalable adjustment ring, the maximum expanding extent of the diameter size of the C-shaped collar can be restricted to further achieve the tightening efficacy of a pet leash when a pet attempts a sudden rush, as well as effectively preventing the pet from escaping from it when it is released.
