Diabetes mellitus is a pervasive chronic metabolic disorder that induces significant structural changes in the gastrointestinal tract (GIT), notably in the duodenal mucosa, with consequent impairment of nutrient digestion and absorption. This study investigates whether a hydroalcoholic cinnamon extract can preserve or restore the histostereological architecture of the duodenum in an alloxan-induced diabetic rat model. Seventy-two adult male Wistar rats were randomly allocated into three groups: non-diabetic control; diabetic untreated and diabetic treated with cinnamon hydroalcoholic extract (60 mg/kg, orally) daily for four weeks. Diabetes was induced via a single intraperitoneal injection of alloxan (180 mg/kg). After the treatment period, duodenal samples were harvested, fixed, processed routinely, and stained with hematoxylin and eosin, and analyzed morphometrically and stereologically for villus height, crypt depth, goblet cell density, and mucosal vascularization (P < 0.05). Diabetes induced significant atrophy of the duodenal villi, reduced villus height to crypt depth ratio, increased crypt depth, and lower goblet cell density. Administration of cinnamon extract significantly mitigated these changes: villus height was restored toward normal levels, goblet cell numbers increased, crypt depth diminished, and mucosal vascularization improved (P < 0.05). These improvements indicate substantial preservative and restorative effects on duodenal structure. Hydroalcoholic extract of cinnamon exerts marked protective and restorative effects against diabetes-induced duodenal damage, likely mediated through antioxidant and anti-inflammatory mechanisms. These findings support its potential role as a complementary therapeutic agent for mitigating gastrointestinal complications associated with diabetes.