Three log samples were scanned with an industrial CT scanner. The CT scanning data were reconstructed in three-dimension by VGStudio MAX software in order to detect interior defects of the log samples. The results showed that the reconstructed volume model of the logs could reveal three-dimensional distribution of the log defects. Therefore, shape and location of the defects could be observed intuitively by virtual log sawing, resulting in precisely measured size of the defects. Yield of high quality lumber and value of precious logs could be maximized.