Disclosed is a substrate for planographic (lithographic) plate, which comprises metal foils with thicknesses of 5 to 100.mu. laminated onto both surfaces of a sheet which has a thickness of 30 to 400.mu., said sheet being obtained by sheet making of a modified polyolefin composite material comprising 100 parts by weight of a modified polyolefin resin graft-modified partially or wholly with an organic silane compound and 5 to 150 parts by weight of mica.