The specific determination of the presence of heavy metals in environmental samples is possible using enzyme biomarkers. ATPase activity has been used as one of the biomarkers for assessing lead toxicity in the aquatic environment. However, there are some problems associated with ATPase biomarker, namely, the lack of selectivity and the lack of sensitivity at high metal concentration . Thus, to increase the specificity of ATPase biomarker through the investigation of biochemical properties of ATPase, we tested the effects of lead on ATPase in the Macrobrachiurn nipponense, which is a common freshwater decapod in Korea, as a representative aquatic target organism under various experimental conditions. Macrobrachiurn nipponense were divided into three groups : normal control group, LC10-lead treated group, LC20-lead treated gruop. These results obtained were summerized as follows : There are two kinds of ATPase, that is sodium/potasium ion dependent ATPase (Na^(+)/K^(+)ATPase) and independent ATPase (Non-Na^(+)/K^(+)in Macrobrachiurn nipponense. Lead inhibited more potently the activity of Na^(+)/K^(+)ATPase than that of the Non-Na^(+)/K^(+)ATPase in all experimental groups. The inhibition pattern of ATPase activity by lead showed a time and dose dependent mode. Also, the activity of Non-Na^(+)/K^(+)ATPase were more rapidly being recovered from lead-intoxicated status than that of Na^(+)/K^(+)ATPase in experinemtal groups. These results suggest that lead has a specificity for Na^(+)/K^(+)ATPase in Macrobrachiurn nipponense and the change of Na^(+)/K^(+)ATPase activity may possibly be used as a more sensitive biomarker of lead pollution in aquatic ecosystem.