Objective: To understand the changing trajectory of quality of life(QOL) during the treatment courses of breast cancer patients during chemotherapy and to investigate the factors in each treatment course that affect QOL.Methods: The M.D. Anderson Symptom Inventory Scale, the Hospital Anxiety and Depression Scale(HADS), and the Functional Assessment of Cancer Therapy-Breast(FACT-B) scale were used to perform a survey on 174 breast cancer patients who received the TAC(docetaxel, Adriamycin, and cyclophosphamide) chemotherapy regimen before postoperative chemotherapy and 5-7 days after each chemotherapy course.Results: The QOL scores of the breast cancer patients were the lowest before the postoperative chemotherapy(81.2 ± 19.6) and the highest after the second chemotherapy course(94.5 ± 14.4). After the fourth and fifth chemotherapy courses, the scores were much lower again, with values of 82.7 ± 13.9and 82.6 ± 13.1, respectively. The scores improved again after the sixth chemotherapy course(93.9 ± 18.7). Furthermore, each treatment course had different related symptoms that affected the QOL of the patients.Conclusions: More attention should be paid to the changing trajectory of QOL of patients in all treatment courses and to the influence of treatment-related symptoms on the QOL of patients; moreover, interventions should be adopted by medical care personnel to increase QOL in cancer patients. Objective: To understand the changing trajectory of quality of life (QOL) during the treatment courses of breast cancer patients during chemotherapy and to investigate the factors in each treatment course that affect QOL. Methods: The MD Anderson Symptom Inventory Scale, the Hospital Anxiety and Depression Scale (HADS), and the Functional Assessment of Cancer Therapy-Breast (FACT-B) scale were used to perform a survey on 174 breast cancer patients who received the TAC (docetaxel, Adriamycin, and cyclophosphamide) chemotherapy regimen before postoperative chemotherapy and Results: The QOL scores of the breast cancer patients were the lowest before the postoperative chemotherapy (81.2 ± 19.6) and the highest after the second chemotherapy course (94.5 ± 14.4). After the fourth and fifth chemotherapy courses, the scores were much lower again, with values ​​of 82.7 ± 13.9 and 82.6 ± 13.1, respectively. The scores improved again after the sixth chemotherap Furthermore, each treatment course had different related symptoms that affected the QOL of the patients. Conclusions: more attention should be paid to the changing trajectory of QOL of patients in all treatment courses and to the influence of treatment -related symptoms on the QOL of patients; moreover, interventions should be adopted by medical care personnel to increase QOL in cancer patients.