Spherulites are grown in such sections as neck, neck end, and bottom center or bottom periphery of a hollow bottle-shaped container of biaxially oriented-blow molded polyethylene terephthalate where the resin is not substantially subjected to orientation, thereby to improve the thermal resistance, stiffness and content resistance of such sections to almost the same extent as the biaxially oriented sections of the container such as shoulder and cylindrical sections thereof. The aforesaid sections of the preformed piece before being blow-molded or of the blow-molded container where the resin is not substantially subjected to orientation are first heated at 120.degree.-180.degree. C. for 3-8 minutes and then annealed at room temperature, with a result that such sections have a spherulite texture of an increased density and are opacified to white or milky white.