PURPOSE: To enhance the mechanical property, durability, uniformity and sealing property of a sealing material.

CONSTITUTION: A composite sheet is made in such a way that a carbon fiber sheet 2 is laminated on at least one surface of a flexible expanding graphite sheet 1. When the surface of the composite sheet is covered with a metal of 650°C or higher in its melting point and having ductility, e.g. nickel or the like, the mechanical strength is enhanced and the oxidizing reaction of graphite or carbon fiber can be prevented, thereby improving the heat resistance. By manufacturing a pre-molded body in winding the composite sheet and effecting compression molding thereto, a sealing material 3 such as a gasket can be obtained which is integrated with the composite sheet. The sealing material 3 is used for a coupling in an internal combustion engine that is likely to be exposed to high temperature.