Objectives: Few reports on breast cancer patients have focused on the younger ages at which breast cancer morbidity increases. The purpose of this study was to clarify the quality of life (QOL) and its related factors in female postoperative breast cancer patients younger than 50 years. Methods: A total of 166 (valid rate 57.8%) female postoperative patients were administered a questionnaire anonymously answered at their outpatient clinics specializing in breast cancer. QOL was evaluated using the QOL Questionnaire for Cancer Patients Treated with Anticancer Drugs (QOL-ACD). Multiple regression analysis of 13 items that showed a significant difference in the total points of QOL-ACD was performed with categories as independent variables and the total points of QOL-ACD as a dependent variable. Results: The mean age of the subjects was 43.6 years. The median total points of QOL-ACD was 88. The multiple regression analysis showed the following seven factors were related to the total points of QOL-ACD: ability to fulfill roles in the family, no symptoms, no financial difficuies, requiring no support at hospital visit, the use of many kinds of stress-coping methods, taking no medication for diseases other than cancer, and not unsatisfied with the scars and shape of breasts. Conclusion: The QOL of young, postoperative breast cancer patients was lower than that of the patient groups that included older subjects. To improve their QOL, it is important to provide social support for their family roles and economic situations, in addition to physical and psychological support based on the characteristics of the disease.