Magnetite Fe₃O₄ and spinel (2:1) and (4:1) NiFe₂O₄ magnetic nanoparticles (MNPs) were prepared by simple and affordable co-precipitation methods using an extract of star anise (Illicium verum) as a green reducing agent. The morphology and chemical composition of these MNPs were confirmed by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, UV–visible spectroscopy, and X-ray diffraction (XRD). The synthesized magnetite Fe₃O₄ and spinel (2:1) and (4:1) NiFe₂O₄ MNPs were in the size range of 0.1–1 µm. The MNPs had irregular clustered platelets (magnetite Fe₃O₄) and pyramidal structures (spinel (2:1) and (4:1) NiFe₂O₄ NPs). The average sizes of the synthesized magnetite Fe₃O₄, and spinel (2:1) and (4:1) NiFe₂O₄ MNPs calculated using XRD analysis were 66.8, 72.5, and 72.9 nm, respectively. In addition to the characteristic absorption peaks of magnetite Fe₃O₄, those of spinel (2:1) and (4:1) NiFe₂O₄ MNPs were detected at ~300–350 nm and ~700 nm, respectively. Overall, the results of this study indicate that the synthesized magnetite Fe₃O₄, and spinel (2:1) and (4:1) NiFe₂O₄ MNPs showed high biomedical activities against liver carcinoma cells and non-small lung adenocarcinoma cells.