Background: Hypertension is the most common cardiovascular disease and a major cardiovascular risk factor that causes significant morbidity and mortality worldwide. Most common type is primary (essential) hypertension and is genetically determined. It affects many systems of the body and can also alter various hematological parameters. The study was undertaken to check the effect of atenolol on hemoglobin (Hb) level in mild to moderate hypertension.Methods: The study was prospective and non-randomized. Thirty newly diagnosed hypertensives selected for atenolol therapy by medicine personnel were enrolled in the study based on inclusion and exclusion criteria. Patients were divided into pre-treatment (before starting atenolol therapy) and post-treatment group. Red blood cell (RBC) count, Hb, packed cell volume (PCV) and red cell indices were measured at the time of enrolment and then monthly after starting atenolol for next 3 months.Result: Results were analyzed by repeated measure analysis of variance. Atenolol treatment was found to increase Hb and PCV significantly, whereas no significant change in RBC count and red cell indices.Conclusions: Treatment with atenolol for mild to moderate hypertension has shown a significant increase in Hb and PCV level. This positive effect may be because of the decrease in sodium and water reabsorption by decrease in sympathetic overactivity and excretion of sodium and water by improvement in kidney functions. Atenolol has no any direct effect on Hb synthesis and erythropoiesis