In this study, the aqueous extract of Acacia caesia leaves was used as a reducing agent and capping agent to synthesize magnetite nanoparticles (Fe3O4) or iron oxide nanoparticles (IONPs). The physicochemical properties of Fe3O4 NPs were characterized using UV-Vis, FTIR, XRD, FESEM-EDX and HRTEM methods, showing that the NPs had a spherical shape with an average particle size of 69 nm. The functional groups responsible for the reduction of Fe3O4 NPs were found using FTIR correlated with phytochemical screening and XRD revealed a face-centered cubic structure. Effective in vitro antifungal, antioxidant, and anti-inflammatory activities of Fe3O4 have been discovered. DPPH antioxidant activity and albumin denaturation inhibition exhibited lower IC50 values than other activities. The cytotoxic activity on HeLa cell lines is considered very effective with an IC50 value of 65.30 µg mL-1.