PURPOSE: To stabilize ethylene or propylene fibers by mixing blue and green phthalocyanine, and red azo pigments into a molten substance forming films or fibers together with the specified stabilizer combination.

CONSTITUTION: Blue and green phthalocyanine, and red (dis) azo pigments of ≤2 phr are mixed into a molten substance forming films or fibers together with a stabilizer. The molten substance is extruded to form monofilaments having a diameter of less than 50 μ or thin films having a thickness of less than 50 μ. Herein, as the above-mentioned stabilizer, (A) piperidyl based hindered amine photostabilizer having the molecular structure contg. two or more multi- substd. piperidyl groups, is used in combination with (B) 3,5-disubstituted-4- hydroxybenzoate of the formula (R10 and R11 are each 1-12C alkyl, phenyl or the like; and R12 is 10-24C alkyl or 4-12C cycloalkyl or the like).