An olefin thermoplastic elastomer composition which is superior in the resistance to oils, heat resistance, formability and flexibility is provided, said elestomer composition comprising the components(A) 40 90 parts by weight of a polypropylene resin having a melt flow rate (determined at 230 .degree. C. under a load of 2.16 kg according to ASTM D 1238) of 0.1 5 g/10 minutes,(B) 10 60 parts by weight of a copolymer rubber based on olefin, the contents of the components (A) and (B) summing up to 100 parts by weight, and(C) 20 150 parts by weight of a softener,wherein the composition is in such a cross-linked state that the gel content thereof amounts to 97% by weight or higher.