A structure of a shoulder strap for a bag is provided to prevent a strap from being separated from a bag in use and to make it easy to exchange the strap. A structure of a shoulder strap for a bag comprises a fixture(102) and a rotator(112) adhered to both sides of a strap. The fixture is adhered to both sides of a bag to detach both end parts of the strap from the bag and is combined with a ball(106) which is elastically supported by an elastic member and protruded to the outside. The rotator is formed of an insertion hole(113) on the center in order to be inserted into the fixture, an insertion hole(115) inserted into the extrusion piece of the fixture, and a guide channel(114) in which balls are inserted.
