The present invention relates to a novel pharmaceutical composition for the preparation of effervescent powders or tablets incorporating ibuprofen or one of its pharmaceutically acceptable salts as the active ingredient.This composition comprises:an effective amount of ibuprofen or one of its pharmaceutically acceptable salts;a pharmaceutically acceptable effervescent system comprising at least one alkaline carbonate and at least one organic acid, preferably in a sufficient amount to give a pH below about 8; andat least one pharmaceutically acceptable antioxidant in a sufficient amount to stabilize the ibuprofen.This composition has a remarkable stability both in powder form and in tablet form.