This study uses green, environmentally friendly methods to synthesize manganese oxide nanoparticles (MnO-NPs) that can be applied on mild steel as a safe and eco-friendly material with corrosion inhibition attributes. Mukia madaraspatana leaf extract is effective in the green synthesis of Mno-NPs. Several critical parameters can influence the corrosion rate and inhibition efficiency of the MnO-NPs, including the dose of nanoparticles in parts per million (PPM), acid concentration, temperature, and exposure time. Response Surface Methodology-Box Behnken Design (RSM-BBD) was employed to optimize these parameters. An optimal dosage of 550 parts per million (ppm) of nanoparticles, an acid concentration of 0.9 M, a temperature of 37°C, and an exposure time of 3.2 hours resulted in an inhibition efficiency of 92.5%. It reduced the corrosion rate to 0.652 (mm/Y) in an independent validation run. These findings demonstrate that the environmentally friendly synthesized MnO-NPs have great potential as an anti-corrosive agent for mild steel.