The heat resistance of the neck of a thin synthetic resin container which is utilised as a packing container of a liq. such as a fruit juice, edible oil, etc., requiring heat-packing, is improved using a multi-layered structure. The neck structure has a multi-layered structure where a thermoplastic resin having higher heat resistance than that of a resin forming the neck is disposed as a heat-resistant layer inside the thermoplastic resin forming the neck of the container. Part of the resin forming the heat-resistant layer is exposed outside the neck forming resin at the open end of the neck, and the open end or the outside of the neck portion including the open end is formed by the same heat resistant resin as that of the heat-resistant layer. The heat resistant layer is extended to the inside of a support ring to improve heat-resistance.
