To provide fibers which retain the excellent heat resistance and flame retardancy inherent in polybenzazole fibers and pyridobisimidazole fibers, have improved post-processability and neither necessitate considerable change in production process conditions nor require a high-temperature and long-time heating treatment. With respect to the polybenzazole fiber and pyridobisimidazole fiber, in an electron diffraction diagram of a surface layer part (from the surface to 1 μm) of the fibers, the fibers containing a crystal present in a state satisfying that S2/S1 is in a prescribed range, wherein S1 is a diffraction peak area derived from a crystal (200) plane and S2 is a diffraction peak area derived from a plurality of other crystal planes along an equatorial direction profile.