Oral composition in the form of gel comprising chitosan, pectin with a high degree of methoxylation, a sugary substance or a polyol, L-carnitine, N-acetyl-cysteine in combination with suitable excipients or diluents for use in the treatment and prevention of gastritis, gastric reflux esophagitis, peptic ulcer lesions and dystrophic lesions of the oral and digestive mucosa membranes with iatrogenic and radiotherapy basis.