PURPOSE: To obtain an optical fiber for facilitating the inspection in optical communication system or the like and an inspection method therefor.

CONSTITUTION: The optical fiber 18 comprises a core 26 where diffraction grating 28 for reflecting the light of specified wavelength is formed while inclining against the optical axis, and a housing 16 being fixed to surround the part where the diffraction grating 28 is formed and provided with an inspection window 20 for passing the light to the diffraction grating 28 or receiving the light therefrom. An optical signal of specified wavelength passes through the inspection window 20 of the housing 16 and impinges on the optical fiber 18. The optical signal is reflected on the diffraction grating 28 and propagate through the core 26. It is reflected again on the diffraction grating 28 and delivered through the inspection window 20 before being processed to locate the trouble point.