Abstract: Objective To compare the characteristics of electrolytes in primary aldosteronism（PA） and essential hypertension（EH）. Methods Characteristics of electrolytes in 202 PA and 67 EH patients admitted to our department from March 2000 to June 2010 were retrospectively analyzed. Results The serum potassium and calcium levels were significantly lower in PA patients than in EH patients（P＜0.01）.The serum natrium,plasma aldosterone,urinary aldosterone levels and CO2CP were significantly higher in PA patients than in EH patients（P＜0.01）.The serum potassium level was lower in PA patients without hypokalemia than in EH patients without hypokalemia（P＜0.01）,while the serum natrium,plasma aldosterone and urinary aldosterone were significantly higher in PA patients without hypokalemia than in EH patients without hypokalemia（P＜0.01）. Conclusion Generally speaking,the serum potassium,natrium,calcium levels and CO2CP are different in PA and EH patients.