Provided is an improved structure of a back clip of a tool box. The tool box induces a main body and a back clip. The main body has a back side in which two slide channels are formed. The back side of the main body is also provided with a spring plate. The back clip has opposite side edges each forming a wing section. The two wing sections are receivable and engageable with the slide channels of the back side of the main body for sliding in a vertical direction. The back clip includes a hanging hole and a retention slot formed therein. With such a structural arrangement, a tool box that is carryable and usable in a hung or attached form is provided.