Pholiota adiposa is an edible chestnut mushroom with many health benefits, such as antioxidant and anticancer activity. In this paper, polysaccharides were extracted from Pholidota adiposa using an acid extraction process. The crude polysaccharide was purified using DEAE-cellulose chromatography, and two polysaccharide fractions of SPAP2-1 and SPAP2-2 were obtained. The structure was characterized using UV, GPC, GC, FT-IR, methylation, and NMR analysis. Monosaccharide component analysis indicated that SPAP2-1 (19 kDa) and SPAP2-2 (20 kDa) contained mannose, glucose, and galactose with different molecular ratios. Their antitumor effects were investigated using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium (MTT) assay, Annexin V-fluorescein isothiocyanate (FITC), propidium iodide (PI) staining, and flow cytometry. By analyzing the changes in the cells, SPAP2-1 caused damage and changed the proliferation rate of HeLa cells. SPAP2-1 showed strong interference to the cell cycle of HeLa cells and induced cell apoptosis. Overall, these results suggested that polysaccharides from Pholiota adiposa, especially SPAP2-1, may have the potential to be used as a tumor cell inhibitor, which needs further study.