The objective of this study was to test the reliability and validity of the Taiwan Chinese version of the EORTC QLQ-C30 (version 3) and EORTC QLQ-BR23. The authors followed the guidelines of translation and pilot testing of the questionnaires. The questionnaires were given to 35 breast cancer patients under active treatment and 54 under follow-up at the National Taiwan University Hospital from November 2000 to October 2001. A retest was conducted one to two weeks after the first interview/form completion for the follow-up group. The intraclass correlation coefficients of the two questionnaires were moderate to high in the follow-up group. The Cronbach's alpha coefficients of most scales of the two questionnaires were > or = 0.70 except that of physical functioning (0.68), cognitive functioning (0.53), and arm symptoms (0.59). Correlations of scales measuring similar dimensions of the EORTC QLQ-C30 and the SF-36 were moderate. Patients in the active treatment group had more serious QOL problems due to disease and treatment. Results of this study showed that the Taiwan Chinese version of the two questionnaires had good test/retest reliability, high internal consistency in most scales, and could show the expected differences between patients in active chemotherapy and follow-up group. Copyright 2003 John Wiley & Sons, Ltd.