Abstract: This experiment focused on the preparation of polysaccharides from jackfruit filum using both acid and alkaline extraction methods. After determining the polysaccharide yield, the structures of the polysaccharides were analyzed and compared using various techniques, including high-performance liquid chromatography, Fourier-transform infrared spectroscopy, ion chromatography, nuclear magnetic resonance, and differential scanning calorimetry. The biological properties of the polysaccharides were evaluated through in vitro assessments of their antioxidant and hypoglycemic activities. The results indicated that the yield of acid-extracted polysaccharide (AcJFP) was lower than that of alkali-extracted polysaccharide (AlJFP). Both AcJFP and AlJFP fractions were composed of monosaccharides such as glucose and galacturonic acid. The weight-average molecular weights were 1.01 kDa for AcJFP and 12.08 kDa for AlJFP. Both fractions contained α and β glycosidic linkages, together with long side chains and numerous branches, and lacked a triple-helical structure. X-ray diffraction patterns revealed differences in the crystalline aggregation structures of the two polysaccharides, while thermogravimetric analysis demonstrated good thermal stability. In vitro biological activity assessments showed that AcJFP exhibited stronger DPPH, hydroxyl, ABTS⁺ radical-scavenging abilities, total antioxidant capacity, and inhibition of α-amylase activity, while AlJFP showed superior ferrous ion-chelating ability. Therefore, the method of extraction impacts both the structure and biological activities of polysaccharides from jackfruit filum.