A joint structure has a first main body, a positioning pin, a second main body, and a controlling button. The first main body forms with an annular wall and a limiting groove, and the annular wall forms an engaging passage. The positioning pin is mounted in the first main body. The second main body has a limiting protrusion and is rotatably mounted on the first main body; the limiting protrusion is mounted on the limiting groove. The controlling button is mounted on the second main body and forms a positioning groove and an engaging block corresponding to the engaging passage. The positioning pin can abut the positioning groove. With the cooperation of the positioning groove and the positioning pin, the joint structure can be folded or unfolded easily.