Plants belonging to the family Amaryllidaceae have been the focus of abundant studies thanks to their structurally diverse alkaloids with excellent biological and pharmacological profiles. Nevertheless, the anti-diabetic properties of these plant species have been considered to a lesser extent, in particular those of the subfamily Amaryllidoideae. Hence, in this work, the potential hypoglycaemic effects of the crude mucilage of Hippeastrum vittatum (L'Her.) (syn. Amaryllis vittata) bulbs were examined at 150 and 250 mg/kg using the streptozotocin-induced diabetic rat model. Overall, as compared to the untreated diabetic rats, oral administration of the mucilage at 150 mg/kg significantly ameliorated the induced hyperglycaemia by 45.37% and 61.95% after 2 and 4 h, respectively, whereas the maximum hypoglycemic actions were observed at 250 mg/kg, causing 57.37% and 65.74% reduction in the elevated blood glucose levels after 2 and 3 h, respectively. These effects were also markedly comparable to those of the standard hypoglycaemic drug gliclazide (50 mg/kg, p.o.). As the first report on the anti-hyperglycaemic activity of the genus Hippeastrum, the obtained results enlighten the potential of the water-soluble polysaccharide fraction from this plant and other Amaryllidaceae species for the development of natural hypoglycaemic agents that could be helpful as alternative or complementary therapies for type-2 diabetes.