Objective To investigate the structural characteristics, in vitro antioxidant activity, and hypoglycemic effects of Plantago seed polysaccharides (PSP) on type 2 diabetes mellitus (T2DM) rats.Methods The structure of PSP is analyzed via ultraviolet (UV) spectroscopy, high-performance gel permeation chromatography (HPGPC), and ion chromatography (IC). Antioxidant activity is assessed by DPPH, ABTS, and hydroxyl free radical scavenging rates. Then, a T2DM rat model is established using streptozotocin (STZ) to assess the effects of PSP on fasting blood glucose (FBG), blood lipids, and oxidative stress markers.Results In an amorphous structure, PSP has a molecular weight of 1.42×10⁴, primarily composed of glucose (Glc), mannose (Man), galactose (Gal), and arabinose (Ara). Additionally, it exhibits high thermal stability. The DPPH, ABTS, and hydroxyl free radical scavenging rates of PSP are 77.50%, 57.76%, and 39.71%, respectively. In animal experiments, PSP significantly reduces FBG, total cholesterol (TC), and triglyceride (TG) levels in T2DM rats (P<0.01), increases superoxide dismutase (SOD) activity, and decreases malondialdehyde (MDA) content.Conclusion PSP exhibits clear structural characteristics alongside potent antioxidant and hypoglycemic activities, suggesting its potential as an adjunctive functional ingredient for diabetes management.