This study aimed to determine the toxicity and maximum allowable levels of selenium (Se-NPs) and iron (Fe-NPs) nanoparticles for the Nereis worm (Hediste diversicolor). This worm is a critical live feed source in sturgeon aquaculture, directly influencing the health and growth of larvae and juveniles. Determining safe dietary levels of nanoparticles in this organism is therefore essential for ensuring the safety of the entire sturgeon feed chain. Worms were exposed to six concentrations (0, 100 μg/kg, 1, 10, 100 mg/kg, and 1 g/kg diet) of each nanoparticle for 96 hours. Throughout the experiment, aeration was provided, and worm behavior was monitored. Cumulative mortality was recorded at 24, 48, 72, and 96-hour intervals. Data were recorded in Microsoft Office Excel 2019, and statistical analysis was performed using SPSS software (Version 20). Data were analyzed by Probit analysis with a 95% confidence level. The LC₁₀, LC₅₀, and LC₉₀ values of Se-NPs were calculated as 291.2 mg/kg, 989.8 mg/kg, and 1.69 g/kg, respectively. For Fe-NPs, these values were 924.3 mg/kg, 3.3 g/kg, and 5.7 g/kg, respectively. This study establishes critical toxicity thresholds for Se-NPs and Fe-NPs in Nereis worms. The findings provide essential data for developing safe feeding protocols in sturgeon aquaculture, helping to prevent potential nanoparticle toxicity transfer through contaminated live feed and ensuring sustainable sturgeon production.