PROBLEM TO BE SOLVED: To provide a multifilament and fiber product in which a particular insecticidal component is retained on the surface thereof by dipping, painting or coating, and to provide a fiber product that has especially an excellent effect on mosquito control.SOLUTION: The present invention provides a multifilament in which 5-chloro-4-ethyl-6-[2-(4-trifluoromethylphenyl)ethylamino]pyrimidine is retained on the surface of a polyester made multifilament. The present invention also provides a fiber product in which 5-chloro-4-ethyl-6-[2-(4-trifluoromethylphenyl)ethylamino]pyrimidine is retained on the surface of a fiber product made using the polyester made multifilament.SELECTED DRAWING: None