Objective This study aimed to optimize the preparation process of selenium nanoparticles stabilized by Atrina pectinata polysaccharides (APPS-SeNPs), evaluate their antioxidant activity, and explore their potential as a functional food additive.Methods Selenium nanoparticles were prepared using the sodium selenite reduction method with A. pectinata polysaccharides as stabilizer. The preparation process was optimized using single-factor experiments and response surface methodology (RSM). The particle size, zeta potential and selenium content were measured, and the nanoscale structure was analyzed. Antioxidant activity was evaluated by assessing the scavenging effects on DPPH and hydroxyl (OH) radicals. Four factors influencing particle size-molar ratio of vitamin C to sodium selenite, reaction temperature, reaction time, and polysaccharide concentration-were analyzed.Results The optimal preparation conditions were as follows: molar ratio of vitamin C to sodium selenite was 8.3∶1, reacting at 44 ℃ for 2.3 hours, and polysaccharide concentration of 0.4 mg/mL. Under the control of these conditions, the selenium nanoparticles size was (69.81±1.04) nm, and the Zeta potential was (-35.28±0.41) mV, with the selenium content at (195.73±0.39) μg/g. The structural analysis confirmed successful selenization, with the nanoparticles exhibiting an amorphous form. Antioxidant assays showed that APPS-SeNPs had significant scavenging effect on DPPH and OH radicals, surpassing both A. pectinata polysaccharides and nano-selenium alone.Conclusion The selenium nanoparticles stabilized by A. pectinata polysaccharides demonstrated excellent antioxidant properties and stability, suggesting their potential as a novel functional food additive.