Type 2 diabetes mellitus (T2DM) is associated with a number of complications, in particular, gastrointestinal tract dysfunction. Impaired mucin secretion by the gastric mucosa in rats with T2DM may affect the absorption of drugs in the stomach and may explain the poor efficacy of treatment and correction of the condition. The aim of our work was to study changes in mucin secretion by the mucous membrane of the gastric fundus in rats with T2DM and the administration of metformin in combination with propionate. T2DM was modelled in rats by a high-fat diet for 3 months with a single administration of streptozotocin (25 mg/kg). Pharmacological correction was performed by intragastric administration of metformin (60 mg/ kg), propionate (60 mg/kg), and combined administration of the mentioned drugs for 14 days. Structural changes in the gastric mucosa and mucopolysaccharide secretion activity were assessed by histochemistry. Western blot analysis of MUC5AC expression was performed. A significant decrease in mucin production was observed in the lower stomach of rats, which was associated with a decrease in the density of cells actively producing acidic mucopolysaccharides. Metformin administration to animals with T2DM did not restore mucin production in the gastric fundus, whereas propionate administration increased acid mucopolysaccharide secretion. An increase in the neutral component of mucus and MUC5AC was found in T2DM. The combined administration of metformin and propionate helped to reduce the content of this mucin. The identified morphofunctional changes in the gastric fundus require further research and should be taken into account when using oral hypoglycaemic drugs because the loss of the mucin barrier layer may affect the state of the gastric mucosa and the absorption of drugs.