To obtain a polyolefin fiber excellent in discoloration resistance, and especially hardly causing the discoloration even if the amount of the mixed antioxidant is increased so that the fiber may be formed at high temperature.

This fiber comprising a thermoplastic polymer obtained by compounding ≥20 wt.% polyolefin as at least one constituent component contains 0.01-1.0 wt.% phenolic antioxidant based on the weight of the polyolefin, and represented by the formula (R1 is a 1-3C alkyl) in the fiber and hydrotalcite in the weight of 0.1-10 times as much as the weight of the phenolic antioxidant.