PURPOSE: To obtain a vessel having excellent gas barrier properties and resistance to plug separation, by a method wherein a thermoplastic resin layer properties is formed between polyester inner and outer surface layers, an adhesive agent resin layer is formed among the thermoplastic resin layer of the gas barrier properties and the polyester inner and outer layers and thermoplastic polyester is injected finally.

CONSTITUTION: Thermoplastic polyester 20 is injected up to the middle of a cavity 3 of the inside of an injection mold. Then the title vessel possesses (A) a core 22 of gas barrier resin selected out of groups composed of ethylene vinyl alochol copolymer whose alcoholic content is 40W85mol% and polyamide containing a xylylene group and possesses (B) the fusion point or the softening point which is lower than that of the said gas barrier property resin by 3°C or more. A composite pellet 21 composed of a sheath 23 of adhesive resin selected out of groups composed of (i) aliphatic series and copolymerized polyamide having a side chain amino group or a dialkyl amino group, (ii) aliphatic series copolymerized polyamide and (iii) polymerized aliphatic series polyamide is injected within the foregoing injection mold after melting of the same. A multi-layer perform 25 whose gas barrier layer 22 has been closed up tightly is formed by injecting thermoplastic polyester 24 finally.