The indication of computed tomotraphy for the breast lesions are 1) Unusually extensive or small breast caused technical difficulties in performing mammograms. 2) Questionable mammographic findings, especially in dense proliferative breast parenchyme. 3) Microcancer. 4) Suspicious regional lymph node enlargement or invasion of the chest wall by breast cancer. The diagnosis of breast CT in breast cancer is based on pathologic anatomic change and characteristic increase of mean CT No. of lesion following contrast enhancement. Authors analysed CT of the 34 patients who were clinically suspected breast cancer, and compared with mammography. The results are as follows: 1. Pathological diagnosis of 34 cases were 27 cases of breast cancer, 4 cases of fibrocystic disease, 2 cases of fibroadenoma, and 1 case of intraductal papilloma. The diagnostic accurcy of CT in 27 breast cancer was 93%(25 cases) and mammography 71%(19 cases). 2. Correct diagnosis of CT in 7 benign breast diseases i in 5 cases and mammography in 5 cases. 3. The most importment finding of CT in breast cancer is characteristic increase of CT No. of lesion following contrast enhancement (200ml, 65%): over average 50HU in 19 cases of 27 breast cancers, 30-50HU in a 6 cases, 20-30HU in 2 cases with tumor mecrosis. 4. Compared with mammography, other more valuable CT findings of breast cancer are axillary lymph node enlargement and adjacentic pectoral muscle invasion. 5. In conclusion, Breast CT is considered as a valuable diagnostic tool in evaluation of breast cancer, but not of benign breast disease.