A thermoplastic polymer composition having good flexibility and excellent barrier properties with respect to gases and organic liquids, which can be adhesively bonded to a polyolefin resin, this composition comprising an ethylene-vinyl alcohol copolymer (A), a polymer mixture (B) composed of a block copolymer (I) mainly comprising a vinyl aromatic polymer block and a conjugated diene polymer block which may be hydrogenated, and a rubber softener (II), and a polyolefin resin (C), wherein at least part of the block copolymer (I) is modified at a modification ratio of 0.05 wt. % or higher so as to have a functional group capable of reacting with the ethylene-vinyl alcohol copolymer (A), wherein the ISO type A hardness of the thermoplastic polymer composition is not less than 30 and not higher than 90, and the oxygen permeation coefficient is 20,000 mL20 .mu.m/m.sup.2dayatm or less.