To investigate the effect of ovalbumin (OVA) encapsulation on the stability and antioxidant activity of polyphenolic compounds, OVA was employed as a delivery carrier that encapsulated hydrophobic polyphenol kaempferol (KAE) and hydrophilic polyphenol tannic acid (TA) as the active compounds. OVA-TA, OVA-KAE, and OVA-TA-KAE composite nanoparticles were prepared, and their physicochemical properties and antioxidant activities were characterized. The results showed that OVA exhibited good encapsulation effects for both KAE and TA. KAE enhanced the thermal stability of the nanoparticles, while TA improved the structural stability and antioxidant activity, thereby enabling better encapsulation by OVA. Particle size, zeta potential, intrinsic fluorescence analysis, Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy indicated that KAE/TA were effectively encapsulated within OVA, with the three types of nanoparticles exhibiting structural stability and uniform dispersion. OVA showed better binding with TA, resulting in the highest protein structural stability and the maintenance of a stable three-dimensional protein structure. Differential scanning calorimetry analysis indicated that KAE enhanced the thermal stability of the nanoparticles' spatial structure. Analyses of total phenol content and antioxidant activity revealed that OVA encapsulation inhibited polyphenol degradation. In particular, OVA-TA-KAE had a total phenol content of 141.33 mg.g-1 and DPPH scavenging activity of 4 909.36 μmol Trolox/g. The results of this study provide novel insights into the loading of KAE/TA in OVA nanoparticles and the effectiveness and feasibility of OVA encapsulation in preserving the antioxidant properties of KAE and TA.