Abstract: The present invention relates to a method of producing an optical fiber-processing phase mask having minimized connection errors that may degrade the spectral line shape and group delay characteristics of an optical fiber diffraction grating fabricated by using the phase mask. The present invention provides a method of producing an optical fiber-processing phase mask having a repeating pattern of grating-shaped grooves and strips provided on one surface of a transparent substrate, so that diffracted light produced by the repeating pattern is applied to an optical fiber to fabricate a diffraction grating in the optical fiber by interference fringes of diffracted light of different orders.