The present invention provides a pharmaceutical composition for treating gastrointestinal diseases comprising ranitidine, sucralfate and bismuth subcitrate as active ingredients and a preparation method thereof. According to the present invention, when a combination drug of ranitidine, sucralfate and bismuth subcitrate is prepared, it is possible to address a hygroscopicity problem of ranitidine and increase formulation stability and drug bioavailability by controlling particle sizes of sucralfate and bismuth subcitrate.
