The estrogen-signaling pathway plays an important role in the pathophysiology of breast cancer, and the sulfotransferase 1A (SULT1A) family has been found to be both downstream targets of tamoxifen and a risk factor of breast cancer. We have used PCR-RFLP and direct sequencing methods to determine SULT1A2 polymorphisms in 230 Taiwanese breast cancer patients. The results showed that the frequencies of SULT1A2*1 and SULT1A2*2 occurring were 94.8% and 5.2%, respectively. No SULT1A2*3 allele was found in these patients. In comparison with the frequency of healthy controls (96.0% and 4.0% for SULT1A2*1 and SULT1A2*2, respectively), the allelic frequencies of SULT1A2 polymorphisms in these patients were not statistically significant (p=0.398). However, the SULT1A2*2 allele seems to influence the age of onset among early-onset breast cancer patients (p=0.021, OR=2.74, 95%CI=1.13-6.65).