Abstract:[Objective] This study explored the structural characteristics and in vitro antioxidant activity of yam polysaccharide-selenium nanoparticle (YP-SeNPs) complexes.[Method] Yam polysaccharide (YP) were obtained through hot water extraction and then purified by purification, diethylaminoethyl cellulose 52 (DEAE-52) column chromatography, and dialysis. With YP as a template, YP-SeNPs were prepared with different Se/YP mass ratios (1∶3, 1∶1, and 4∶3) in an oxidation-reduction system comprising ascorbic acid (VC) and sodium selenite (Na2SeO3). The complexes were characterized via multiple techniques, including visual observation of solution color, ultraviolet-visible absorption (UV-vis) spectroscopy, particle size measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The in vitro antioxidant activity of YP-SeNPs was evaluated by measuring the scavenging ability against 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) free radicals.[Result] YP-SeNPs were successfully constructed, exhibiting spherical morphology and containing C, O, and Se elements. The optimal Se/YP mass ratio was determined to be 1∶3, yielding the smallest particle size of (61.67±0.69) nm. The complexes demonstrated high stability. YP effectively prevented the aggregation and sedimentation of SeNPs, thereby improving the dispersion of the complexes. YP-SeNPs exhibited good scavenging capacity against DPPH and ABTS free radicals, with the maximum scavenging rates of (96.66±0.79)% and (96.66±1.19)%, respectively.[Conclusion] YP-SeNPs have good antioxidant activity and can be developed and utilized as a functional antioxidant.