We undertook to translate and cross-culturally adapt the Functional Assessment of Cancer Therapy-Breast (FACT-B) scale into Korean and to evaluate its reliability and validity. The translation procedure followed the standard Functional Assessment of Chronic Illness Therapy translation methodology. A total of 201 breast cancer patients (mean age, 43.87 years) were studied for psychometric properties of the FACT-B scale. A pre-test of 20 Korean breast cancer patients indicated that the Korean FACT-B scale provided good content coverage and overall comprehensibility. Our results indicated high internal consistency of the FACT-B scale, with Cronbach's alpha coefficients ranging from 0.79 to 0.90. The only exception was the Breast Cancer Scale (BCS), which had a Cronbach's alpha coefficient of 0.67. We can consider that most of the patients in this study had not resumed sexual activity after surgery and found it difficult to comment on this aspect. We also considered that contents of the BCS may have been somewhat heterogeneous. After performing a factor analysis of the BCS data from this study, we identified three factors, accounting 58.8%: psychological distress (5 items, with explained variances of 27.5%), feminine satisfaction (2 items, with explained variances of 17.1%), and physical complaints (2 items, with explained variances of 14.2%). The FACT-B scale also demonstrated good convergent and divergent validity when correlated with the shortened forms of the Profile of Mood States and the Functional Living Index-Cancer (FLIC). We can now evaluate the Quality of Life (QoL) of Korean breast cancer patients using this reliable and valid instrument. Nevertheless our study has the limitation that it did not evaluate the sensitivity to the changes of the patients' QoL in the long term follow-up, and we will supplement it in our further study.