Abstract: A replaceable arm structure for spectacles comprises a joint unit disposed between a frame and an arm. A front end of the joint unit is pivotally connected to the frame, and a rear end of the joint unit forms a horizontal spindle perpendicularly connected to a radial locating shaft. A horizontal axial hole and an axial cutout slot communicating with a radial locating slot perpendicularly are formed on a front end of the arm. The rear end of the joint unit is pivotally connected to the arm by fitting the horizontal spindle with the horizontal axial hole. The rear end of the joint unit and the arm are fixed together by fitting the radial locating shaft with the radial locating slot.