Provided is a threaded joint for heavy-walled oil country tubular goods which can acquire both the ensuring of sealability and the prevention of galling in a state where a high external pressure is also applied to the threaded joint in addition to a high compressive force. A surface of a pin 3 side which forms a seal portion 13 and a surface of a box 1 side which forms a seal portion 11 are formed into a convex curved surface and a tapered surface respectively. With respect to the pin 3, a seal thickness t s of the pin is set to 15 mm or less, a shape parameter t s /D (D: outer diameter of a pin raw pipe portion) is set to 0.045 or more, and a complete thread length ratio L/t (L: complete thread length of the pin, t: wall thickness of the pin raw pipe portion) is set to 4.0 or less.
