MDR1 gene encodes a gp-170 membrane protein which acts as a energy-dependent pump to transport anticancer agents out of the cells. In this article, we briefly summarize the MDR gene family, gene amplification, gene expression by differentiation and gene expression in clinical tumors. We also describe the characterization of the promotor and tissue specific enhancer of the MDR1 gene and our recent study of the regulatory mechanism of this gene expression.