Abstract: Two optical fibers 10, 20 to be spliced are prepared (FIG. 1A), coatings of resin 12, 22 are removed from end portions of the respective optical fibers 10, 20 to expose glass fibers 11, 21 (FIG. 1B), the glass fibers 11, 21 are aligned each other (FIG. 1C), and a fusion step is carried out to heat the end faces of the glass fibers 11, 21 to cause fusion thereof to form a fusion-spliced portion A (FIG. 1D). After that, a thermal-strain-removing step is carried out to remove thermal strain by a heating treatment of a wider region R2 than a heated region R1 of the fusion-spliced portion A, at a temperature of not less than 500° C. nor more than 1500° C. (FIG. 1E).