Abstract: An inorganic board is obtained by extrusion molding of raw material composition, contains cement and silica-containing material in weight ratio ranging from 45:55 to 55:45, contains 3 to 8 wt %, with respect to total solids, of organic fibers. In the inorganic board, specific gravity ranges from 1.4 to 2.0, flexural strength is not lower than 20 N/mm2, dimensional change rate upon ten-day moisture release at 80° C. is not greater than 0.1%, dimensional change rate upon seven-day moisture absorption is not greater than 0.1%, seven-day dimensional change rate in an environment having carbon dioxide concentration of 5% is not greater than 0.1%. A method for producing the inorganic board comprises the steps of producing raw material composition that comprises cement, silica-containing material and organic fibers; producing mat by extrusion molding of the raw material composition; and subjecting the mat to autoclave curing at 140 to 200° C.