Breast cancer is the most common cancer among women worldwide and second in Thailand. Glutathione S-transferase (GST) enzymes involved in the detoxification of reactive metabolites of carcinogens may be important in modulating susceptibility to cancers. This study aimed to determine the influence of genetic polymorphisms of glutathione S-transferase T1, M1, P1 and A1 on breast cancer in Thai patients. Links with clinico-pathological characteristics were also analyzed. The results showed no association between GSTs polymorphism and overall susceptibility to breast cancer in Thai patients (P < 0.05). However, the data pointed to a relation of the GSTP1(Ile105Val) polymorphism with progesterone receptor status (P = 0.04) and age at diagnosis (P = 0.03) of breast cancer cases. In summary, this is the first study to report associations between glutathione S-transferase T1, M1, P1 and A1 gene polymorphisms and breast cancer in Thai patients. While GST genotypes may not be associated with susceptibility, a GSTP1 polymorphism (Ile105Val) may be related to progression of breast cancer.