PURPOSE: To maintain brilliant colors and glossiness by mingling glassy micro- particles carrying insecticide into thin color fibers of a pile group composed of more than two different color fibers so as to prevent the insecticide from being decomposed or eluted by moisture or the like.

CONSTITUTION: Since insecticide is carried by glassy microparticles is used, when the insecticide such as boric acid is mingled into resin for spinning fibers, and when thus obtained mingled fibers are used as synthetic turf, the insecticide can be prevented from being decomposed or eluted by moisture or the like. Meanwhile, when the glassy microparticles are mingled into the fibers, the brilliance and gloss of color yarns formed from the fibers are likely to be lowered and to be turbid. However, when pile yarns having a predetermined color tone are composed of fibers having more than two colors including a thick color thicker than the predetermined color tone and a thin color thinner than the predetermined color tone, the glassy particles are mingled into the thin color fibers. Further, no glassy microparticles are mingled into the thick color fibers, and accordingly, the brilliant color and the gloss which are excellent in its entirety can be maintained. Accordingly, the pile yarns formed of the fibers has an excellent external appearance.