The effect of temperature on the dielectric properties of rubber wood were investigated in three anisotropic directions-longitudinal, radial, and tangential, and at different measurement frequencies. Low frequency measurements were conducted with a dielectric spectrometer, and high frequencies used microwave applied with open-ended coaxial probe sensors. Dielectric constants and dielectric loss factors were measured at temperatures from 25 to 100°C. A large dielectric dispersion occurred at frequencies less than 10 Hz and at temperatures more than 60°C. The minimum peak value of the dielectric loss factors shifted towards higher frequencies at higher temperatures in all three grain directions. The tangential direction showed the highest activation energy. The dielectric constant decreased as frequency increased from 1 to 10 GHz, and thereafter remained unchanged with additional frequency increases. The dielectric constant exhibited higher values at higher temperatures. The dielectric loss factor showed a peak value at around 10 GHz at 25°C
