The invention discloses a pharmaceutical composition for preventing and/or treating peptic ulcer, including American ginseng or the extract thereof, and a method for preparing American ginseng extract, said method including extracting American ginseng with water or ethanol aqueous solution, and then ultrafiltrating, dialyzing, precipitating with ethanol, or performing reverse phase chromatography to obtain various fractions of extract with anti-peptic ulcer effect.