The most important factor for breast augmentation is to dissect the accurate size of implantation pockets. This study was performed to investigate the anatomical association of the pectoralis major muscle(PMM) with the female breast shape for improving the success rate of mammoplasty. This study included 60 women(120 breasts) in their twenties to thirties who were imaged by CT between September 2006 and December 2007. On reconstructed 3D CT images, 6 points in the area of the PMM were selected as fiducial points, and the PMM contour and the correlation of the PMM with the nipple were analyzed using the imaginary lines connecting individual points. As the volume increased, the lateral and inferior borders of the PMM moved to the superomedial side from the nipple. As the ptosis degree increased, the density became lower, and the lateral and inferior borders of the PMM moved to the superomedial side of the nipple. However, there was no significant correlation between age and PMM contour. The results of this study suggest that the PMM contour may change according to the volume, ptosis and density of the breast. This study can provide objective information for breast surgery, thereby increasing the success rate of mammoplasty.