The green microalga genus is mostly comprised of species that exhibit a wide range of salinity tolerance, including inhabitants of hyperhaline reservoirs. Na content in cells inhabiting saline environments is maintained at a fairly low level, comparable to that in the cells of freshwater organisms. However, despite a long history of studying the physiological and molecular mechanisms that ensure the ability of halotolerant species to survive at high concentrations of NaCl, the question of how cells remove excess Na ions entering from the environment is still debatable. For thermodynamic reasons it should be a primary active mechanism; for example, via a Na-transporting ATPase, but the molecular identification of Na-transporting mechanism in has not yet been carried out. Formerly, in the euryhaline alga , we functionally identified Na-transporting P-type ATPase in experiments with plasma membrane (PM) vesicles which were isolated from this alga. Here we describe the cloning of two putative P-type ATPases from , HA1 and HA2. Phylogenetic analysis showed that both ATPases belong to the clade of proton P-type ATPases, but the similarity between HA1 and HA2 is not high. The expression of HA1 and HA2 in cells under hyperosmotic salt shock was studied by qRT-PCR. Expression of gene decreases and remains at a relatively low level during the response of cells to hyperosmotic salt shock. In contrast, expression of increases under hyperosmotic salt shock. This indicates that HA2 is important for overcoming hyperosmotic salt stress by the algal cells and as an ATPase it is likely directly involved in transport of Na ions. We assume that it is the HA2 ATPase that represents the Na-transporting ATPase.