PURPOSE: To obtain the title synthetic fiber having extremely improved color tone by adding silver-substituted antimicrobial zeolite to a polymer before completion of polymerization and further supplying an alkali halide thereto before spinning.

CONSTITUTION: To a polymer such as polyamide or polyester at a stage prior to completion of polymerization, silver-substituted antimicrobial zeolite is added and an alkali halide such as potassium iodide or potassium bromide is supplied to the polymer before spinning to form a polymer composition containing 0.01-1.0wt.% based on the polymer of the zeolite and 0.001-1.0wt.% of the alkali halide. Then the polymer composition is subjected to melt spinning to give the objective fiber exhibiting excellently antimicrobial performance against Staphylococcus aureus, fungi belonging to the genus Candida, Escherichia coli, etc.