The rise of medical expenses is a common problem in the whole- wide world. All those countries implementing National Health Insurance have been anxiously looking for solutions, and clinical pathway has been found to be the most effective tool to control the growth of medical expense and maintain the quality of healthcare. This study focuses on the development and implementation of clinical pathway of breast cancer who underwent modified radical mastectomy, and investigate the impact of implementation of clinical pathway on the control of the length of stay, inpatient medical care expenditures, healthcare quality, and patient¡¦s medical satisfaction. The 90 patients of MRM before implementation ( July 1999 to Sep. 2000 ) and 80 patients after implementation ( Jan. 2001 to Feb. 2002 ) are taken as the targets of this study. The major findings of the study are listed as follows: 1. Clinical pathway can reasonably control the length of stay. 2. Clinical pathway can reduce inpatient medical care expenditures. 3. Clinical pathway can improve healthcare quality. 4. Clinical pathway can improve patient¡¦s medical satisfaction. 5. Clinical pathway can influence doctor¡¦s partial practice pattern. Finally this study concludes that clinical pathway is an instructive tool for hospital management. Based on the results and discussion from the study, we suggest the implementation of clinical pathway cones best in conjunction with the impact of case payment; besides, the quality of medical care should be assured under the controlled medical cost.