Abstract: SGP-2 was an acidic polysaccharide with good hypoglycemic activity isolated from Sarcandra glabra (Thunb.) Nakai in the previous study. This study used the laser particle size analysis, transmission electron microscopy (TEM) and atomic force microscopy(AFM) analysis techniques to analyze the advanced structure of SGP-2 in the deionized water and Na₂SO₄ solution and discuss the structure-activity relationship between the advanced structural characterizations and the α-glucosidase inhibition activities of SGP-2 and its derivative in vitro.Results showed that SGP-2 presented aggregates and spheres in the deionized water.AFM analysis showed that the diameter of SGP-2 was 33 nm and the height was 1.84 nm, whereas compact spherical conformations with high degrees of branching were observed in 0.05 mol/L Na₂SO₄ solution and SGP-2 had smaller particle size in saline solution compared with that in water.SGP-2 treated by 0.5 mol/L urea and dialysis at the concentration of 1 000 μg/mL showed 98.8% inhibition activity of that from untreated SGP-2. The inhibition rate of short rod conformation with branches reached 83.3% when the temperature rose up to 140 °C, and the α-glucosidase inhibition activity was even higher than that of untreated SGP-2 under the same condition; while SGP-2 with the tangled glycan chains under the condition of carboxyl group reduced had much lower inhibition activity.Therefore, the spherical structure or the short rod conformation with branches played an important role in the activity of SGP-2. This research provides a theoretical basis for further study of structure-function relationship between the advanced structure and activity of polysaccharides.