Gel-forming mucins are large high-molecular weight secreted O-glycoproteins responsible for the gel-properties of the mucus blanket. Five orthologous gel-forming mucins have been cloned in human and mouse. Among them, the mucin MUC6 has been less studied, particularly in rodents and no anti rodent-Muc6 antibody has been reported yet. In order to further study Muc6 in mice, our aims were to obtain a specific Muc6 antibody, to validate it and to test it in Cftr deficient mice. A polyclonal serum named CP4 was isolated from a rabbit immunized by a mouse Muc6 peptide. In Western blot experiments, the antibody detected a high-molecular weight molecule secreted by the gastric tissue. Using immunohistochemistry, we showed that the antibody reacted strongly with deep glands of duodenum and ileum and mucous neck cells of gastric body. CP4 also recognized Muc6 protein secreted at the surface of the stomach and renal collecting tubules. The centroacinar cells of pancreatic tissue also reacted with the antibody. Cftr-/- mice showed a higher expression of Muc6 at both protein and RNA levels compared with their control Cftr+/+ littermates suggesting that as in the human disease, Muc6 may contribute to the formation of materials that block pancreatic acini and ducts in mouse models of cystic fibrosis. The rabbit anti-mouse Muc6 polyclonal antibody seems highly specific to the mouse mucin and will be useful to study pancreatic pathology in cystic fibrosis.