PURPOSE: To provide a producing method of a biaxially orientated blow-molded plastic vessel which is excellent in heat and pressure resistance and design.

CONSTITUTION: A plastic parison 20 composed of the opening 21, the body 22 and the bottom 23 is made and molded by orientation blow molding in the state that a part corresponding to the upper part of the vessel body in the parison 20 is retained in a temperature higher by 0-20°C than other parts. In this way, the upper part and the lower part have almost the same thickness and a primary blow-molding 30 having the lower part with a larger diameter than the diameter of the upper part is formed. Next, the lower part and the bottom of the primary blow-molding are contracted at 130-200°C and the obtained contracted molding is again treated by orientation blow-molding to produce a heat and pressure resistant vessel with an aimed shape.