Provided is an insecticidal composition that has a wide insecticidal spectrum, is highly active, enables a reduction in the amount of an active ingredient to be applied, and has a long-lasting effect. Also provided is an insect pest control method. The insecticidal composition contains, as active ingredients, (A) at least one organic phosphorus compound selected from the group consisting of fosthiazate, imicyafos and cadusafos, and (B) fluensulfone. The insect pest control method applies respective effective amounts of (A) and (B).
