To obtain a thermoplastic elastomer especially having impermeability suitable for using as stoppers of chemicals with satisfactorily maintaining properties such as heat resistance, molding ability and the likes.

This thermoplastic elastomer is obtained by dynamically vulcanizing a resin composition comprising 3-20 wt.% of a butyl-based rubber, 10-60 wt.% of a hydrogenated aromatxc vinyl-conjugate diene compound copolymer having ≥150,000 number average molecular weight and 20-60 wt.% of a mineral oil with a vulcanizing agent.