Potassium channels are important for many physiological functions in plants, one of which is to regulate plant adaptation to stress conditions. In this study, a K(+) channel PutAKT1 cDNA was isolated from the salt-tolerant plant Puccinellia tenuiflora. A phylogenetic analysis showed that PutAKT1 belongs to the AKT1-subfamily in the Shaker K(+) channel family. PutAKT1 was localized in the plasma membrane and it was preferentially expressed in the roots. The expression of PutAKT1 was induced by K(+)-starvation stress in the roots and was not down-regulated by the presence of excess Na(+). Arabidopsis plants over-expressing PutAKT1 showed enhanced salt tolerance compared to wild-type plants as shown by their shoot phenotype and dry weight. Expression of PutAKT1 increased the K(+) content of Arabidopsis under normal, K(+)-starvation, and NaCl-stress conditions. Arabidopsis expressing PutAKT1 also showed a decrease in Na(+) accumulation both in the shoot and in the root. These results suggest that PutAKT1 is involved in mediating K(+) uptake (i) both in low- and in high-affinity K(+) uptake range, and (ii) unlike its homologs in rice, even under salt-stress condition.