Abstract: A biaxially stretched, blow molded bottle made of a resin comprising at least one of polyethylene terephthalate and a copolymerized polyester comprising ethylene terephthalate. The bottle neck is formed, just as the bottle body is formed, by expanding a body of a preform in a shape of a test tube in a stretching step of the molding process. The bottle neck has an average thickness in a range of 0.6 to 1.8 mm, and at the bottle neck, the resin is partially crystallized and is in an oriented crystallized state. A ratio of an absolute value of crystallization enthalpy, ?Hc, to melting enthalpy, ?Hm (|?Hc|/?Hm) of the bottle neck is a value less than 0.1, and a rate of dimensional change in the outer diameter of the bottle neck is 0.2% or less.

Abstract: A biaxially stretched, blow molded bottle made of a resin of the PET series has a bottle neck that is formed by expanding a body of a preform in a shape of a test tube to give the bottle neck a large diameter, just as the preform is expanded to obtain a body of the bottle, in a stretching step of a biaxial stretching and blow molding process. The bottle neck density is set at 1.368 g/cm3 or more or a ratio of an absolute value of crystallization enthalpy, ?Hc, to melting enthalpy, ?Hm, (that is, |?Hc|/?Hm) is set at a value less than 0.1, by meeting a processing condition for stretching in a stretching step and by setting a predetermined mold temperature within a thermally crystallizable range used for the resin of the polyethylene terephthalate series.