Boron, is an essential microelement that plays a role in plant and animal development. However, an excess amount of boron is toxic for both types of organisms.The yeast Saccharomyces cerevisiae is an ideal model organism for describing the mechanism and regulation of metal ion transport in eukaryotes. We screened a yeast genomic DNA library to find genes that confer boron resistance to wild-type cells.Thirty transformants were isolated that were able to grow in the presence of a toxic amount of boron and all of them contained the multidrug efflux transporter gene ATR1 (YML116w) in the expression cassette. Our subsequent analysis revealed that ATR1 deletion mutants (.atr1) were sensitive to boron treatment and hyper-accumulated boron inside cells, whereas wild-type cells overexpressing the ATR1 gene were resistant to boron and hypoaccumulated boron in cells. We also analysed the global gene expression pattern in response to boron treatment and found that expression of ATR1 is upregulated along with many other transporter and amino acid biosynthesis genes. Our data suggest that the ATR1 gene functions as a boron efflux pump and is reqired for boron tolerance in yeast cells.