Ulcerative desease is one of the most frequent pathologies of digestion system. Approximately five percents of population have ulcers of the stomach or duodenum. Chronic stomach ulcers may be pre-cancerous. A well known antiulcerative drug, Omeprazole, is a direct H⁺/K⁺ ATPase inhibitor. It acts as a proton pump blocker, and thus increases stomach lumen pH. Recent data reveal antioxidative features of Omeprasole and its relatives (Biswas, 2003, Blandizzi, 2005). Our aim was to estimate Omeprazole treatment (OT) effect on rat stomach mucosa morphofuctional state during ulcer healing. Cold stress induced stomach ulcers were developed as described in (Biswas, 2003). Omeprazole was administered intraperitoneally in dose of 0.8 mg/kg body weight. Ulcer index was calculated in mm2; and the acidity of stomach lumen content was measured. The cold stress induced two patterns of stomach ulceration in control animals: first one with small number of large ulcers, second - with large numbers of small ulcers. The second pattern was prevalent on first and second day after stressing in OT group. OT significantly increased pH of stomach contents. The number and area of ulcers in animals subjected to Omeprasole injections were reduced compared with non-treated rats (40 minutes after stressing - 36,5% less, 1 day after cold stress - 46,04%, 2 days - 26,67%, 3 days - 22,56%, 4 and 5 days - no effect). We thank Dr.Charles F.Babbs for critical reading the abstract.