The membrane-bound ATPases were separated on sucrose gradient from corn roots and characterized by pH optima, sensitivity to monovalent salt, Km and Vmax. The pH optima for the activity of all the ATPases associated with 13,000g pellet and 13,000∼80,000g pellet were 5 and 9, respectively. The ATPases in Fractions B and C of the 13,000g pellet were more active at pH 4 than pH 9. While, in the case of Fractions D, E and F, they were reverse. The activities of the ATPase in Fractions A and C of the 13,000∼80,000g pellet were greater at pH 5 than pH 9. On the other hand, the ATPases in Fractions B, D, E, and F were more active at pH 9 than pH 5. The optimum concentration of ATP for the assay was about 3 to 5mM. The Km`s for the membrane-bound ATPases in 13,000g pellet and in 13,000∼80,pppg pellet were 0.25mM. While Vmax values for 13,000g pellet were from 8.0 to 12.5 μM Pi/㎎ protein/hr, according to pH values, those for 13,000∼80,000g pellet were from 35.7 to 55.6 μM Pi/㎎ protein/hr. Activities of the membrane-bound ATPases in both 13,000g pellet and 13,000∼80,000g pellet were stimulated with increasing the concentration of K^+.