To provide a manufacturing method of a very thin wall seamless metal pipe by a cold-rolling process using an inclined rolling method, which manufacturing method can remarkably extend the manufacturable range of the seamless metal pipe to the thin wall side.

The method for manufacturing the very thin wall seamless metal pipe employs an inclined rolling mill in a cold-rolling process of the seamless metal pipe. In the method, remarkable thickness reduction can be achieved by reducing the wall thickness, while extending the diameter of a mother pipe, using a plug or a tapered mandrel as an inner surface restricting tool. Especially, the very thin wall seamless metal pipe having a wall thickness of about 0.5 to 0.6 mm can be relatively easily obtained by reheating the small diameter thin wall seamless metal pipe manufactured by a hot-rolling process, and by hot-rolling the thin wall seamless metal pipe using the inclined rolling mill so as to extend its diameter, and by carrying out a cold-rolling operation again using the inclined rolling mill for the thin wall seamless metal pipe as a mother pipe so as to extend its diameter.