A thermoplastic elastomer composition prepared by partially crosslinking a composition comprising the following components (A), (B) and (C):(A) 30-70 parts by weight of an ethylene/.alpha.-olefin copolymer prepared by copolymerizing ethylene and an .alpha.-olefin having 3 to 12 carbon atoms in the presence of a catalyst comprising a solid component and an organoaluminum compound which solid component contains at least magnesium and titanium, said ethylene/.alpha.-olefin copolymer having the following properties (I) to (IV):______________________________________ (I) Melt index 0.01-100 g/10 min (II) Density 0.860-0.910 g/cm.sup.3 (III) Maximum peak not lower than 100.degree. C. temperature as measured according to a differential scanning calorimetry (DSC) (IV) Insolubles in boiling not less than 10 wt. % n-hexane ______________________________________ (B) 70-30 parts by weight of a propylene polymer; and(C) 70-200 parts by weight, based on 100 parts by weight of the components (A) and (B), of an ethylene/.alpha.-olefin copolymer rubber.