Optical fiber specimens with and without polymer surface coating (stripped) were tested under tensile and two-point bending. Their fracture surfaces were evaluated. A distinctive fracture mirror region can be seen at the fracture origin of every stripped fiber failed under stress. Using the known relationship equation between the fracture stress and mirror radius, the fracture mirror constants for the stripped optical fibers subjected to tension and bending were determined to be 1.3 and 9.4 MN m(3/2), respectively. However, the fracture mirror region of as-received optical fiber (with polymer coating) cannot be found from the fracture surface. The fracture hackle marks directing to a fracture initiation flaw are observed. The mirror region formation in bare glass fiber may shed a light for the mechanism of environmental assisted crack growth. (C) 2003 Elsevier B.V. All rights reserved.