An eco-friendly and sustainable approach for the synthesis of manganese dioxide (MnO?) nanoparticles was developed using Bunium persicum seed extract as a natural reducing and stabilizing agent. The green-synthesized MnO2 nanoparticles were characterized using UV–Vis spectroscopy, FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX), confirming their crystalline nature, nanoscale dimensions, and high purity. The catalytic efficiency of the prepared MnO2 nanoparticles was evaluated in organic transformation reactions, where they exhibited excellent activity under mild conditions. In addition, preliminary biological studies demonstrated notable antimicrobial activity against selected bacterial strains. The results highlight the dual catalytic and biological potential of biosynthesized MnO2 nanoparticles and emphasize the advantages of plant-mediated nanomaterial synthesis in green chemistry and sustainable nanotechnology