Bioequivalence of two oral formulations of Atenolol 100 mg was studied in 24 healthy volunteers by a single-dose, two-treatment, twoperiod, randomized, crossover design with a one-week washout period between the two phases of the study and under fasting condition. After dosing, serial blood samples were collected for a period of 36 hours. Plasma harvested from blood was analyzed for atenolol by a sensitive, selective, reproducible and accurate LC - MS/MS method. Various pharmacokinetic parameters including AUC0-1, AUC0-~, Cmax, Tmax and T1/2 were determined for the both formulations by its plasma concentrations. 90 percent confidence interval for test/reference ratio of AUCo-~. Cmax were found within acceptance range of 80-125 percent. Based on these statistical inferences, the two formulations were of acceptable bioequivalence.