Two novel polysaccharides, MAPS and MRP5A, were obtained from the root of Panax notoginseng using column chromatography. Structure characterization suggested that MRP5A, with an average molecular weight of 11.38 x 10(4) Da, was composed of rhamnose (7.7%), arabinose (6.6%), glucose (69.8%) and galactose (15.9%). MRP5 had an average molecular weight of 9.16 x 10(4) Da and consisted of rhamnose (3.6%), arabinose (14.5%), glucose (51.2%) and galactose (29.7%). The results of methylation analysis and one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectra reveal that MRP5 contains repeating units of -> 3)- beta-Glcp-(1 ->, -> 3)-beta-Galp-(1 ->, -> 3, 6)-beta-Galp-(1 ->, -> 3)-beta-Galp-(1 ->, -> 3, 6)-beta-Galp-(1 ->, -> 3)-alpha- Rhap-(1 ->, -> 3)-alpha-Araf-(1 ->, and alpha-Araf-(1 -> residues. MRP5 and MRP5A exhibited relatively low antioxidant abilities in vitro, but strongly protective effects against oxidative stress and lifespan extension effects in C. elegans. Overall, the present study indicated that MRP5 could be further investigated as a functional food for promoting healthspan.