A mixed polymer liquid is prepared by mixing a polycarbosilane-dissolved organic solvent with poly(methylsilane) and moderated to viscosity of 5 20 Pas by heat-treatment to promote partial cross-linking reaction. The mixed-polymer is then melt-spun to fiber at 250 350.degree. C. The fiber is cured by treatment at 100 200.degree. C. in an oxidizing atmosphere, and baked at 1000.degree. C. or higher. Due to thermosetting action of poly(methylsilane), the mixed polymer liquid is continuously melt-spun without breakage, and SiC fiber produced in this way is useful for reinforcement of SiC composite excellent in toughness, strength and heat-resistance.