An aqueous oral mouthwash solution containing the monosodium salt of carbonic acid with alkalinizing and antimucositis activities. Upon introduction into the mouth, the sodium bicarbonate dissociates, forming sodium and bicarbonate ions, which buffer excess hydrogen ion and elevates the oral pH. An alkaline oral environment is less prone to colonization with yeast and aciduric bacteria. In addition, this solution may help relieve mucositis and mucositis-induced pain by diluting human saliva, and cleansing and lubricating mucosal tissues of the mouth, tongue and oropharynx.