Abstract: To solve problems of a conventional process for producing a ceramic sheet by extrusion such that it is a production process with a prolonged lead time requiring material granulation and homogenization steps and if homogenization of a kneaded clay is insufficient, the dispersion of the density of a green sheet will occur and a ceramic sintered body after firing will have deformation or warpage, thereby to cause failures in circuit pattern printing and joining between a metal circuit board and a heatsink. A process for producing a ceramic sheet comprising use of an extrusion molding machine combining a twin screw extruder with powerful kneading performance and a single screw extruder with molding stability, so that a quality equivalent to or superior to that of the prior art can be obtained and that high production efficiency can be attained, and a ceramic substrate utilizing it, are obtained.