Optical fibers are composed of the core and the cladding that are covered by the polymer coating to protect them from subsequent handling damage. Sometimes, this polymer coating, however, should be removed to fabricate optical devices involving the optical fiber such as Bragg gratings, optical couplers, optical sensors and optical connectors. In general, the mechanical stripper is used to remove this polymer coating. In this case, the mechanical stripper may cause mechanical defects on the surface of the optical fiber and also, mechanical defects make the optical fiber weak. We have researched relationship between these mechanical defects and the residual stress gradient in the optical fiber. We have made a mechanical defect on the surface of a single mode fiber with a mechanical blade and measured the residual stress distribution along the axial direction of the optical fiber. From this research, we have observed that at the position with the mechanical defect, the residual stress in the core was converted to the compressive residual stress (about 15MPa) and the residual stress in the cladding was converted to the tensile residual stress (about 7MPa). We have demonstrated that the mechanical defect on the fiber surface can cause the gradient of the residual stress distributions in the optical fiber and also, measurement of the residual stress distribution in the optical fiber can be used as a tool to find out the mechanical defects on the optical fiber.