PURPOSE: The titled composition, obtained by copolymerizing ethylene, etc. with a nonconjugated cyclic diene in a specific proportion, and specifying the melt index (MI) thereof, having a high density and melt tension, and capable of giving films having improved bubble stability, external appearance and strength.

CONSTITUTION: An ethylenically unsaturated copolymer composition obtained by copolymerizing ethylene or ethylene and another α-olefin with a nonconjugated cyclic diene, e.g. 2,5-norbornane, and having 0.05W1.5wt% diene content, ≤5wt% another α-olefin content, 0.955W0.968g/cm3 density and 0.01W0.3g/10min melt index (MI). For example, given amounts of the ethylene, α-olefin and nonconjugated cyclic diene are copolymerized in the presence of a Ziegler type catalyst under conditions of 50W95°C and 0.5W15kg/cm2 pressure to give the aimed composition.