Abstract: An improved universal joint for use on a leash for dogs is provided with a hook element, a rotary connector, a retaining tube and a sleeve. The rotary connector has a ball-shaped joint head and an extended engaging rod. The universal joint is fixedly combined with a hook element that is engaged with the retaining tube by way of a pin shaft. The retaining tube has an open end and a semi-open and roundly cornered dome-shaped end having a through hole. The rotary connector is led through the through hole of its engaging rod with the ball-shaped joint head confined in the retaining tube. The engaging rod having a central deep cavity for receiving the front tip of the leash so that the leash and the rotary connector can be punched to fix together. The ball-shaped joint head and the roundly cornered retaining tube permit the rotary connector and the leash to operate smoothly at a wide range of angles so as to effectively avoid abrasion and deformation of the retaining tube and the rotary connector in operation.