The CT digital radiography is a new accurate technique for measuring the long bone length. Authors performed a comparative study on accuracy, time and film consumption and radiation dose between conventional spot scanogram and CT scanogram. We used two femur and two tibia speciment for materials, the Somation II(Siemens) for CT scanogram,and Rad Check (Victoreen) for radiation dosmetery. There was no significant difference in accuracy between direct measurement , conventional scanogram and CT scangram(lesser than 1 % difference). The examination time of conventional scanogram was about 35 minutes. CT was 15 minutes, and the film consumption of spot scanogram was 3 of 14 $ imes$17〃size, but the CT scanogram need only one 8 $ imes$10〃film for completion of study. The radiation dose of hip , knee and ankle joint were 220 mRad , 365 mRad, respectively, in spot scanogram, but it was lesser than 5 mRad in all joints in CT scanogram. The advantages of the CT scanogram are simple, rapid and r duced radiation.