Azadirachta indica mediated selenium nanoparticles (A. indica (Se NPs)) have garnered interest due to their potential anti-inflammatory and antioxidant properties. This study aimed to evaluate the anti-inflammatory and antioxidant activities of A. indica (Se NPs) and their cytotoxic effects using various assays. A. indica (Se NPs) were synthesized and characterized. The anti-inflammatory activity was assessed using BSA, EA, and Membrane Stabilization assays, while antioxidant activity was evaluated using DPPH, H2O2, and FRAP assays. The cytotoxic effect was determined using a brine shrimp lethality assay. A. indica (Se NPs) exhibited dose-dependent anti-inflammatory effects in all assays, with comparable efficacy to diclofenac sodium. The antioxidant potential of A. indica (Se NPs) was demonstrated through scavenging of free radicals and protection against oxidative stress. The cytotoxicity study revealed a dose-dependent decrease in survival rates of brine shrimp nauplii with increasing concentrations of SeNPs. The findings suggest that A. indica (Se NPs) possess significant anti-inflammatory and antioxidant activities, making them potential candidates for therapeutic applications. The dose-dependent response observed in the assays indicates the importance of concentration in eliciting biological effects. The cytotoxicity results highlight the need for further investigation into the safety profile of SeNPs. In conclusion, A. indica mediated selenium nanoparticles exhibit promising anti-inflammatory and antioxidant properties, with a dose-dependent response observed in their biological activities. Further research is warranted to elucidate the mechanisms of action and potential clinical applications of A. indica (Se NPs) while ensuring their safety for therapeutic use.