A sheet material for a radio wave absorber and a radio wave absorber formed from the sheet material, where the sheet material is light weighted and has excellent form-retaining capability and workability for field assembling. A sheet material (1) for a radio wave absorber has a corrugated paperboard structure with an undulated corrugated medium (2) and a planar liner (3) that are layered over each other. The corrugated medium (2) and/or the liner (3) are constructed from a sheet including an electrical-loss material. A radio wave absorber (10) is characterized in that the sheet material (1) for a radio wave absorber is cut, folded, and assembled as a hollow three-dimensional structure body, which has a shape of wedge, polygonal pyramid, or polygonal cylinder.