PURPOSE: To obtain the title composition excellent in flame retardancy, flexibility, heat resistance and mechanical strengths, by mixing a specified ethylenic copolymer with a flame-retarding filler.

CONSTITUTION: Ethylene (a) is copolymerized with an unsaturated carboxylic acid (ester) (b) in the presence of a polymerization catalyst (c) based on a transition metal compound and an organo-metallic compound and a Lewis acid (d) to obtain an ethylenic copolymer (A) of a weight-average MW≥5,000, containing units of formula I and 0.001W45mol.% units of formula II (wherein R1 is H, a halogen, a 1W20C alkyl, a 3W20C alkenyl, a 3W20C cycloalkyl, a 6W20C aryl or a 7W20C aralkyl, R2 is H, a 1W20C alkyl or a 7W20C aralkyl, an n is 0W20) arranged at random in the linear polymer chain and having an m.p. satisfying formula III (wherein b is the molar % of units of formula II, and Tm is it m.p.). 100pts.wt. component A is mixed with 10W160pts.wt. flame- retarding filler (B) [e.g., Mg(OH)2].