AbstractUltrasonic tests were performed in the main directions at 300 kHz in poplar and spruce reaction wood and normal wood. The experiments were conducted on 2 x 2 x 10 cm3 specimens selected from the pith to the bark. The same phase velocity values were measured in poplar tension wood and normal wood. In compression wood, the phase velocity was lower in the longitudinal direction and higher in the transverse direction. The group velocity measured in the longitudinal direction in tension wood was greater than in normal wood, but lower values were obtained in compression wood in comparison to those obtained in normal wood. The results showed that wave attenuation cannot be significantly affected by the structural properties of reaction wood. A better wave energy transfer pathway (RMS voltage) was found in poplar and spruce reaction wood than in normal wood. Acoustic radiation in reaction wood of both species was lower than levels obtained in normal wood in all anisotropic directions. The results obtained when comparing reaction wood and normal wood of both species indicated that sound velocity decreased as moisture content increased, but the attenuation coefficients increased slightly.