PURPOSE: To prevent the degradation in strength by receiving damages on surface and to provide the surface suitable for combining with a matrix by coating the surface with an inorg. compd. and metal.

CONSTITUTION: The surface of this oxynitride glass fiber is coated with ≥1 kinds of the inorg. compd. and the metal. The surface treatment of the oxynitride glass fiber varies largely with the mating matrix to be combined with the glass fiber. The surface is coated mainly with the inorg. compd. by a surface treating agent essentially consisting of a film forming agent, coupling agent, surfactant, lubricant, antistatic agent, etc., in the case of combining the fiber with plastics, rubber or cement. On the other hand, the surface is treated by an electroless plating, CVD method, etc., of the metals, such as Ni, Sn, and Ta or inorg. compds., such as TiC, ZrC and SiC in the case of combining the fiber with the metals or ceramics.