PURPOSE: To obtain the above composition having remarkably improved water resistance, free from generation of toxic halogen-containing gas in combustion and suitable as an insulation material and sheath for electric wire or cable, by plating red phosphorus with metal by electroless plating and using the plated red phosphorus as a flame retarding assistant.

CONSTITUTION: The objective composition is produced by compounding 100pts. wt. of a polyolefin (e.g., ethylene-propylene copolymer) with (A) 30W300pts.wt. of an inorganic flame-retardant (e.g., aluminum hydroxide or magnesium hydroxide) and (B) 0.5W30pts.wt. of electroless metal-plated red phosphorus (the metal is Ni, Fe, etc.).