A sheet material for shielding electromagnetic waves, characterized in that it consists of a soft, elastic, coarse, porous mat-like material formed by intertwining a plurality of conductive fibers (4) into a cotton-like material; and a method of constructing an electromagnetic wave shielding, comprising the steps of intertwining a plurality of conductive fibers (4) into a soft, elastic, coarse, porous mat-like electromagnetic wave shielding sheet material (2), and forming electromagnetic wave shielding by putting the sheet material (2) on the outer surface of a member, which defines a chamber in which electromagnetic wave shielding is to be formed, in such a manner that the above-mentioned outer surface as a whole is covered therewith to enclose the chamber as a whole. When this sheet material (2) is put on walls, floors, ceilings, and surfaces defining narrow space and clearances, a reliable electromagnetic wave shielding can be formed.