Salinity is one of the important abiotic stresses which affecting growth and performance of plants. A Plant’s response to salinity depends on the genotype, salt intensity and duration of the stress. Plant sodium transporter activity is the most important salt tolerance mechanism in plants. In the present study, the expression pattern of the Na+ transporter gene was investigated in roots of three barley genotypes (Sahara3771, an Iranian advanced line (A line) as a salt-tolerant cultivar  and Clipper as salt-susceptible) by quantitative real-time-PCR. The plants were exposed to 0, 100 and 200 mM NaCl at the seedling stage and root samples were harvested 24 hours, 3 days and 3 weeks after salt treatment. Also, root length, wet and dry weight were measured. The results indicated that root fresh and dry weight decreased with increasing salt concentration and duration of treatment. Analysis of variance revealed significant differences of Na⁺ transporter gene expression among the genotypes with respect to salinity levels and sampling stages. Salinity x genotype, salinity x sampling stage, genotypes x sampling stage and salinity x genotype x sampling stage were all significant. Increased expression of the gene was associated with salt tolerance in the genotypes. In response to 100 and 200 mM NaCl, the mRNA level of Na⁺ transporter gene decreased in Clipper. In Sahara3771 and the A-Linen gene expression decreased and increased respectively in response to 100 and 200 mM NaCl. Under 200 mM NaCl treatment, gene expression in A-Line increased more strongly than in Sahara3771. The results suggest that in these genotypes, salinity tolerance is related to greater ability to sequester Na⁺ into sub-cellular compartments.