Metallic materials to be coated on hollow dielectric THz waveguides were experimentally evaluated. Among six materials examined herein, Cu and Au exhibited highest transmittance for 2.5-mm-long parallel-plate waveguides, whose thicknesses necessary to compete bulk perfect electric conductor were also equivalent, 65 and 75 nm, respectively. The oxide layer natively formed on Cu surface did not impact the transmittance. Therefore, Cu had equal potential with Au, and would be the principal material considering its cost and availability.