Recently, a new ultrasonic CT system has been developed as the NDE method suitable for wood. In this system, several characteristics related to the ultrasound traveling in the woods such as the anisotropy of woods, existence of immature woods and ultrasound diffraction in the woods are considered during image composition process. In this study, we inspected the system that had been newly developed for the decayed wood specimen. We performed the ultrasound measurements to reconstruct the CT image. And then, we verified the distributions of each characteristic in the section by measuring the moisture content, specific gravity and compressive strength after cutting the measured specimen by small specimen again. The acquired results are compared with the CT image acquired in the same section. As a result, it is determined that it is possible to detect the locations and sizes of decayed parts in the wood by using the developed ultrasound CT system. In particular, the results show that the initial decays that the weight loss rate is less than 10% and the strength loss rate is less than 30% are also detectable.