A toothbrush for a pet dog is disclosed, in which a groove is longitudinally formed in a center of a head in a direction of a handle, and a cushion material is provided in a surrounding surface, a lower surface and the groove. When a pet dog bites a toothbrush with teeth during a tooth brushing, it is possible to prevent teeth from fracture while preventing a lot of pain occurring when teeth collide with a hard toothbrush. Toothbrush hairs planted in a head are shaped depending on a tooth shape of a pet dog, so it is possible to reliably brush off plague attached on the upper side of a cervical ridge of premolars and molars of a pet dog without applying over stimulation on the gum.