PURPOSE: To improve the transmission characteristics and mechanical strength by using a composition consisting of a specified amount of crystalline polyamide resin and/or polyamide elastomer and a specified amount of an acid modified olefin copolymer as a coating material.

CONSTITUTION: An optical fiber core is coated with a composition consisting of 99W50pts.wt. crystalline polyamide resin and/or polyamide elastomer and 1W 50pts.wt. acid modified olefin copolymer as a coating material by extrusion molding or other method. The resulting coated optical fiber is flexible, is easy to bundle, and has superior mechanical characteristics such as wear resistance and bendability. The fiber causes hardly optical transmission loss.