ATPase was the most available phosphatase in culture broth of 5. coli P90C. To measure the stable phosphatase activity it was necessary to react nth reaction reagent over 30 min and then we can get stable optical density at 410 m. Transfer time from preculture to main culture for the production of $eta$-glactosidase was good after 3 hrs cultivation. Phosphatase activity was highest at log phase in main culture and as the cell begins to make $eta$-galactosidase phosphatase activity begins to decrease.