Microgramma squamulosa (Kaulf.) Sota (Polypodiaceae) is commonly used as an antiulcer agent in the state of São Paulo, mainly in the upper land. The present work aims to study the antiulcer action of the crude extract of the plant rhizome and its toxicity. The effective dose was determined through acute ulcer induction test by stress. Using a determined dose, we performed a test against ulcer through acute induction by ethanol and hydrochloric acid, using cimetidine and misoprostol as reference drugs in both tests. The same extract, its ethanol and ethanol + water (1:1) fractions and the reference drug cimetidine were tested through subchronic induction test with acetic acid. The subchronic toxicity test was performed using a dose of 800 mg/kg of the crude extract, orally administered for 30 days. Finally the extracts and fractions were analysed in order to determine the main chemical groups of substances.