Abstract: In this study, selenium-rice protein peptide nanoparticles were prepared using rice protein peptides as stabilizers and ascorbic acid (V_C) to reduce sodium selenite (Na₂SeO₃), with the particle size, polydispersity index, and Zeta potential serving as indicators for evaluation. To optimize the preparation conditions, a combination of single-factor and orthogonal experiments was performed to determine the molar concentration ratio of V_C to Na₂SeO₃, amount of rice protein peptide added, reaction time, and reaction temperature. Preliminary structural analyses of the nano-selenium were performed using scanning electron microscopy and Fourier-transform infrared spectroscopy. Additionally, the stability of the nano-selenium was investigated under different pH conditions, ion supplementation, and storage at 4 and 25 °C. The results revealed that the optimal preparation conditions were a V_C:Na₂SeO₃ molar concentration ratio of 4:1, the addition of 5 mg/mL rice protein peptide, a reaction time of 5 h, and a reaction temperature of 25 °C. Under these optimal conditions, the average particle size, polydispersity index value, and Zeta potential value of the nano-selenium were 92.00±2.68 nm, 0.104±0.008, −37.20±2.52 mV, respectively. The selenium-rice protein peptides nanoparticles were characterized by a three-dimensional network structure with the nano-selenium particles dispersed within. The system was established to be stable under alkaline conditions, more sensitive to Ca²⁺ than to Na⁺, and remained stable for 35 days at 4 °C. The findings indicate that this material would be suitable for selenium supplementation at room temperature but not for high-temperature processing. This study provides theoretical support for the high-value utilization of rice protein resources and serve as a basis for the further research and development of selenium-rice protein peptides nanoparticles.