Dielectric measurements at 9.8 GHz. and 2.45 GHz were made for the three hardwoods Euramerican hybrid poplar, alder, and oriental beech. The method used was based on Von Hippel's transmission line method. The measurements were carried out at room temperature of 20degrees-24degreesC. The dielectric properties of the wood species were determined for the three principal structural directions at six different moisture conditions, covering the range of 0% to 28% moisture content. Results indicated that the behavior of all wood species studied is quantitatively similar. In general, the dielectric properties increase within the range studied with rising moisture content. The grain direction of the wood also plays a significant role.