Abstract: This study is done to find out the effects of atenolol on plasma electrolytes sodium, potassium, calcium and on serum enzymes, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) of common rabbits Oryctolagus cuniculus following the administration of an oral daily dose of 0.6 mg atenolol for 27 days. Observations showed a non-significant rise in sodium concentration, a significant elevation and ultimate fall of potassium concentration and reduction of calcium levels significantly to half of the normal values. These findings suggest the diuretic action of drug; possibly the prolonged use cause the renal dysfunction. Long-term treatment of hypertension by atenolol may impair the hepatic function indicated by significant very low and high levels of serum AST and ALT, respectively.