Abstract: A fraction enriched in plasma membrane from Dunaliella salina was obtained by apueous two-phase partition system (dextran T500/polyethylene glycol 3350),with high quality and purity.The K_m of plasmalemma ATPase was found to be 0.58 mmol/L,its V_max was 43.59 μmol Pi/(mg protein·h) and the optimum pH 7.5.Enzyme activity was stimulated by the increase of concentration of MgCl₂,CaCl₂ and KCl,but much higher concentrations had a little inhibitory effect.The plasmalemma ATPase exhibited great sensitivities to vanadate,dicyeclohexyl carbodiimide (DCCD),SH regent N ethylmaleimide (NEM),especially to diethylstibestro (DES),whereas it was insensitive to azide,nitrate,molybdate and cyanide.The ATPase activity was notably increased following hyperosmotic shock,and its possible role in osmoregulation was discussed.