The physicochemical properties, structural features and immunomodulatory effects of the white asparagus (Asparagus officinalis L.) skin polysaccharides (WASP) were systematically studied. WASP showed a pectic-like structure with a relatively low degree of esterification (DE, 18%); the weight-average molecular weight (Mw) and intrinsic viscosity were 76.1 kDa and 13 mL/g, respectively. Structurally, the dominated sugar residue of WASP was 4-α-D-GalpA (39.7 mol%), while other residues including α-L-Araf, 3-α-L-Rhap, 2,4-α-L-Rhap, and 4-β-D-Galp were also detected with a comparable amount. A proposed structure of WASP was also presented. Physiologically, WASP could modulate the immune response of RAW 264.7 macrophages through increasing the release of immune factors (IL-6, TNF-α and IL-10) and improving the expression of mRNA. To conclude, the pectic-like polysaccharides from white asparagus (Asparagus officinalis L.) skin could be potentially used as an immunomodulatory agent in functional food.