This morphological study was performed on the stomach of ducks at 6, 12, 18 months after feeding the6% of sulfur in diet and control fed the same diet without sulfur. After weighting of body of 36 ducks,we sacrificed the ducks and harvested stomach. Then we check the fed materials and the lumen of stomach.H-E, alcian blue - PAS (pH 1.0), and alcian blue - PAS (pH2.5) stains were used to histological andhistochemical observation for the mucus The body weights decreased dependent upon the duration offeeding sulfur statistically, however, the stomachs kept their weight except the 18 month fed group.Ulcerative papillae containing caseous necrotic region were conspicuous on the lumen of proventriculus ofsulfur-fed ducks. In addition, some lobules of proventricular glands adjacent to the papillae were observedwith severe atrophy. mucus secreted from mucous epithelium showed same pattern between control andsulfur-fed ducks, but the ducts of proventricular glands in 12, 18 months groups had nonsulfatedmucopolysaccharides. Gizzard had no pathological changes, however, ingested feed were mixed withre-fluxed bile juice from duodenum. Gastric glands in the gizzards of sulfur-fed ducks had increased thenumber of acidic mucin positive cells as well as surface cells containing PAS positive materials, which werethought to bring the change of matrix that observed with strong purple color. These data suggest that sulfurfeeding for long term causes the damage on the proventriculus mucosa and its glands and also the changeon the cuticle secreted from giazzard glands. These changes may be related to decrease of body weight.