Beta adrenergic receptor antagonist drugs (beta blockers) are widely used in treatment of hypertension and in other cardiovascular diseases and also used in treatment of childhood migraine. In U.K and France the annual consumption of Atenolol for a person is 0.63 and 0.3 g respectively. Atenolol can be found in surface waters, waste waters and even in ground waters up to mu g/1 levels. Physio-chemical measurements are not enough for the assessment of environmental impacts of chemicals or pollutants. Toxicity tests with the organisms can be useful tools in environmental studies. As the embryonic stage is more sensitive to pollutants and other stressors, experiments on the embryos are important for assessing the environmental effects of pollutants. The embryonic stage of organisms is important both for ecosystem health and for future of the population. In this study the effects of atenolol on sea urchin (Arbacia lixula) embryo development was evaluated. Sea urchin embryos were exposed to increasing concentration of Atenolol (1,25, 5, 20, 40, 80 and 100 ppm) under static conditions. Embryotoxicity was assessed on 72 h-old pluteus larvae under light microscope. According to obtained results, an increase in larval malformations as skeleton deformities at the pluteus stage were observed and the calculated EC50, for embryotoxicity was 66,46 mg/l.