In the folk-medicine, several kinds of crude drugs are used as diuretics. Twenty three kinds of diuretic drugs were chosen, and examined for their effects on the horse kidney (Na++K+)-adenosine triphosphatase (ATPase), which is an intrinsic enzyme of the plasma membrane and responsible for the active transport of Na+ and K+ across the membrane. Twenty one out of twenty three kinds of ethanol extracts of diuretic drugs inhibited the kidney (Na++K+)-ATPase activity. The intensity of the inhibition of these drugs was compared by estimating the amounts of their ethanol extracts which inhibited the (Na++K+)-ATPase activity by 50% (I50, μg/ml). Among these drugs, Atractylodis Lanceae Rhizoma ( ?? ??, I50=12.8) Atractylodis Rhizoma ( ?? ??, I50=15.2), Plantaginis Semen ( ?? ?? ??, I50=16.0), Plantaginis Herba ( ?? ?? ??, I50=16.0) and Alismatis Rhizoma ( ?? ??, I50=22.0), have strong inhibitory effects on the kidney (Na++K+)-ATPase activity. The ethanol extracts of the rhizomes of Atractylodes lancea DE CANDOLLE ( ?? ?? ?? ?? ) and Atractylodis japonica KITAMURA ( ?? ?? ?? ) were examined with varying concentrations of ATP and ouabain. The mode of inhibition of these two extracts on the (Na++K+)-ATPase activity appeared to be uncompetitive with respect to ATP as judged from Line-weaver-Burk plot. The ethanol extract of Atractylodes japonica KITAMURA decreased the I50 for ouabain from 1.6×10-7 to 7.0×10-9M, while that of Atractylodes lancea DE CANDOLLE did not change the I50 for ouabain.