Disclosed is a thermoplastic elastomer composition excellent in the injection fusion bondability and the surface gloss, which comprises (1) an amorphous ethylene/.alpha.-olefin copolymer (a) and (2) (i) a lowly crystalline copolymer (b) of propylene with an .alpha.-olefin having at least 4 carbon atoms, (ii) a polymer (d) composed mainly of 1-butene or (iii) a combination of the copolymer (b) or the polymer (d) with a crystalline polymer (c) composed mainly of propylene, wherein the component (1) is present in an amount of 10 to 95% by weight based on the total amount of the components (1) and (2), the component (2) is present in an amount of 5 to 90% by weight based on the total amount of the components (1) and (2), and the component (1) or the components (1) and (2) are partially crosslinked.The partial crosslinking is effected by grafting of a radical-polymerizable monomer having at least two polymerizable groups.