The patent application relates to an expander harness tor walking pets on a leash, comprising a back part equipped with a lining, to which a back strap equipped with a buckle portion is attached, and a limiting element fixed to the lining by a limiting element fixing point on the axis line, which is threaded through a leash connector suitable tor connecting a leash, and furthermore there is a shoulder part element on both sides of the axis line, arranged symmetrically, surrounding the neck and/or chest of the dog, threaded through a shoul-der part connecting element, and on the s ide of the shoul- der part connecting element opposite to the shoulder part elements a shoulder part limiting element is fixed together with a shoulder part elastic element.