The significance of postoperative chemotherapy was studied in 439 cases of unilateral primary breast cancer which were proved histologically with no axillary lymph node metastasis. The survival rate was analyzed by life table method. The prognosis of node negative breast cancer patients was mainly associated with tumor size. 10 year survival rate of patients with tumor less than 3 cm treated operativel and by operation combined with chemotherapy was 92.60% and 94.13% respectively. If tumor size was larger than 3 cm, the ten year survival rate of the patients treated operatived was 79.89%, and that of the patients with combined theropy 96.02%. The prognosis was statistically different between the two groups. As to age, status of menopause, pathologral type, kind of surgery and status of ER, the prognosis of patients treated by combined therapy was better than that of patients treated by operation alone. The postoperative chemotherapy was not significantly beneficial to breast cancer patients with tumor less than 3 cm.