To obtain the subject antimicrobial synthetic fibers free from uneven thickness, etc., capable of forming more uniform web and nonwoven fabrics by adhering chitosan salts and a specific modified polyetherester on the surface of fibers.

This fibers are obtained by adhering 0.05 to 5.0 wt.%, based on the fiber weight, of chitosan salts (chitosan lactate, chitosan malate, chitosan adipate, etc.), and 0.05 to 1.0 wt.%, of modified polyetherester expressed by formula R1O-(CO-R2-COO-CH2CH2O-)a-{CO-R2-COO-(CH2CH2)n-}-R3 (R1 is H or CH2CH2OH; R2 is a residue of a dibasic acid; R3 is a 1-12C alkyl; a/b=2/8 to 8/2) (molecular weight; 1,000 to 100,000), affording the antimicrobial synthetic fibers low in static charging in carding process, etc.