It is important to determine the changes in alveolar bone during periodontal treatments. At present, radiography is widely used to determine the changes. But small changes in alveolar bone cannot be detected on X-ray films. To detect these small changes, a direct observation system using gamma-ray from 133Ba was considered. Using a multi-channel analyzer, gamma-ray absorption through the bone was detected in this method. This method was compared with densitometric measurement on the films using sliced animal bone. The newly developed method detected the bone changes more accurately. To evaluate the influence of soft tissue, Mix-D was used in both measurements. 133Ba absorptiometry showed that soft tissue did not influence the measurement more than the densitometric method.