Pathological proliferation of Brgnners gland is rare, and its wide range of morphologieal variations have led to confusing the terminology with considerable lack of agreement. Six cases of duodenal nodular lesions which consisted of pathological proliferation of Brunners glands were examined by light microscopy. Polypectomy was made in two cases, and the remaining 4 cases were examined with endoscopic biopsy materials. Two polypectomy specimens, 2 cm and 3 cm each in great diameters, consisted of protruded ovoid mass with broad and short stalks. Microacopically, all of 6 cases revealed thin strands of fibrous connective tissue which separated the normal-looking Brunners glands in lobules. Individual lobules were composed of groups of acini formed by cuboidal cells admixed with occasional endocrine cells. Presence of glandular and ductal configuration of the Brunners gland aside from thick, randomly arranged bundles of smooth muscle were featured without distinct relation to interlobular septa. Also, one polypectomy case disclosed the nests of fat cells interspersed with the glandular acini. One mucosal biopsy case contained not only the smooth muscle bands but also the intimate mixture of both acini and ducts. We conclude that some of heterogeneous composition of duodenal nodular proliferation of Brunners gland is indicative of a hamartomatous growth.