A process for production of a thermoplastic elastomer composition by melt-kneading a mixture in one step to thereby conduct dynamic crosslinking, wherein the mixture comprises a hydrogenated block copolymer (a.sub.1) which is prepared by hydrogenating a block copolymer comprising a vinyl aromatic polymer block (A.sub.1) and a conjugated diene polymer block (B.sub.1) and has number-average molecular weight of 200000 or above and, if necessary, a non-hydrogenated block copolymer (a.sub.2) comprising a vinyl aromatic polymer block (A.sub.2) and a conjugated diene polymer block (B.sub.2), and contains a non-aromatic rubber softening agent (b), a peroxide-crosslinkable olefin resin (c) having a density of 0.94 g/cm.sup.3 or above, a peroxide-decomposable olefin resin (d), an organic peroxide (e), and a crosslinking aid (f), the amount of (b) being 50 to 250 parts by mass per 100 parts by mass of the sum of (a.sub.1) +(a.sub.2), the amount of (c) being 2.5 to 50 parts by mass per 100 parts by mass of (a); and the amount of (d) being 0.5 to 10 times that of (c) by mass.