In this study, Lactobacillus plantarum M616 and Saccharomyces cerevisiae CICC 32883 were used in modifying Chinese yam polysaccharides (CYPs) through fermentation. The carbohydrate content of microbe-fermented CYP (CYP-LS) was 78.49 % ± 1.64 %, versus the 71.03 % ± 2.75 % carbon content of unfermented CYP (CYP-NF). However, CYP-LS had a lower protein content (6.01 % ± 0.08 %) than CYP-NF (8.24 % ± 0.19 %). The molar ratios among rhamnose, arabinose, galactose, glucose, and mannose were respectively 0.493:0.6695:0.9738:0.7655:12.4365 for CYP-NF and 0.2849:0.182:0.5684:1.4069:3.7227 for CYP-LS. Molecular weight and polydispersity decreased respectively from 124.774 kDa (CYP-NF) to 34.111 kDa (CYP-LS) to and from 6.58 (CYP-NF) to 5.176 (CYP-LS). Moreover, CYP-LS had better immunomodulatory activity than CYP-NF, regulating superoxide dismutase, catalase, glutathione peroxidase, malondialdehyde, tumor necrosis factor-α, interleukin-1β, interleukin-10, and transforming growth factor-β in a RAW 264.7 cell model. A combination of CYP-LS and probiotics (Lactobacillus helveticus HH-LPH17, Lactobacillus johnsonii LBJ 456® and Lactobacillus acidophilus HH-LA26) showed enhanced immune activity.