Breast cancer has recently become the most common cancer in Korea. Although traditional epidemiological approaches, which are defined as "the study of the distribution and determinants of disease frequency in human population" have increased the understanding of breast cancer development in the human population, it cannot address the importance of the genetic susceptibility of humans to this disease. Therefore, a molecular epidemiological study which uses biological or genetic markers to identify and characterize the disease with the help of advances in molecular biology and human genetics might provide a better understanding of the multi-factorial or multi-step occurrence of human breast cancer. The susceptibility genes involved in the pathogenesis of breast cancer have been categorized into two groups: high penetrance genes (i.e., BRAC1, RB, etc.) and low penetrance genes (i.e., GSTs, XRCC1, etc.). This paper addresses the usefulness of biomarkers in epidemiological research of breast cancer and provides examples of the use of selected low penetrance genes involved in breast carcinogenesis in Korean women. Molecular epidemiological studies of breast cancer have enormous potential in helping researchers understand the gene-environmental interactions involved breast carcinogenesis and provide valuable insights into disease progression and survival.