A cement-based composition for extrusion molding which is obtained by adding 0.1-1.5 parts by weight of an extrusion aid, 15-45 parts by weight of water, and 0.01-2.0 parts by weight of a copolymer having a composition comprising 50-99 wt.% structural units (a) derived from a polyoxyalkylene derivative represented by the general formula (1), 1-50 wt.% structural units (b) derived from a dicarboxylic acid represented by the general formula (2) or maleic anhydride, and 0-30 wt.% structural units (c) derived from other copolymerizable monomer to 100 parts by weight of a mixture comprising a hydraulic substance, an aggregate, and fibers.