The aim of this study was to establish an objective method for quantitative evaluation of bone volume change after sinus augmentation. 11 sinuses in 9 patients were evaluated by computed tomography images taken before treatment (T0), and 3 months (T1) and at least 1 year (T2) after sinus augmentation. Based on the 3D digital subtraction technique, augmented bone images were extracted and bone volumes were calculated from voxel numbers of the extracted images. The mean augmented bone volumes at T1 and T2 were 2.46 cm3 and 1.85 cm3, respectively. These bone volume changes were statistically significant and the mean bone volume change ± SE was -24.8% ± 6.1%. Loss of augmented bone was observed in all except one of the patients. The correlation coefficient between bone volume change and elapsed time was -0.64, which was statistically significant and indicated that bone resorption progressed with elapse of time after sinus augmentation. The authors' method of analysis enabled visualization of augmented bone and objective assessment of bone volume change. Within the limited number of cases, the present investigation demonstrated a significant decrease in augmented bone volume between 3 and 23 months after surgery.