In this study, magnetite nanoparticles (Fe₃O₄ NPs) were synthesized using Baccaurea ramiflora leaf extracts and characterized by visual observation, UV–Vis, FTIR, XRD, FESEM, and EDS. The UV−Vis spectrum showed continuous absorption at 300–500 nm, confirming the formation of Fe₃O₄ NPs. FTIR revealed that compounds containing the O-H group act as reducing agents during Fe₃O₄ NPs formation. Agglomerated spherical NPs were observed in the FESEM image. The prominent peak at ~6.4 keV in the EDS spectrum ascertained the existence of Fe, while the sharp peak at ~0.53 keV confirmed the presence of elemental oxygen. XRD patterns affirmed the crystalline nature. The size of as-synthesized NPs was observed to be 8.83 nm. The catalytic activity of Fe₃O₄ NPs for the reduction of methylene blue (MB) dye was monitored by UV–Vis. The maximum absorption peak of MB dye at 664 nm was almost diminished within 20 min, which revealed Fe₃O₄ NPs could be an excellent catalyst for wastewater treatment.