Omeprazole, a substituted benzimidazole, is a specific and noncompetitive inhibitor of the enzyme H+/K+-ATPase, known as the gastric proton pump. It is unstable in conditions of low pH and must be protected from the effects of gastric acid when given orally; thus, it is administered in the form of enteric-coated dosage forms. In this present study, various coating solutions were prepared in different concentrations and applied to previously subcoated omeprazole tablets to examine whether this coating prevented omeprazole from degrading in acidic media. Dissolution tests were conducted in acidic and basic media to determine the appropriate coating ratio. For stability evaluation, an accelerated stability test was performed on developed tablet formulations and commercially obtained capsules. Samples were examined with regard to visual appearance, omeprazole content and dissolution properties for a month. For formulation consideration, the most promising results were obtained from HPMCP4 and CAP(4) (4% enteric coating with hydroxypropylmethyl cellulose phthalate solution and cellulose acetate phthalate solution, respectively) subcoded preparations. From the stability aspect only Losec capsules (Astra-Turkey, commercial product) seem to be dependable.