In the present study, spirugenic iron oxide nanoparticles (SIONs) were biosynthesized using a new simple, expeditious and benign approach which was achieved by combining ferric chloride with Spirulina platensis water extract. SIONs were inspected using UV spectroscopy on 290nm. The Transmission Electron Microscope (TEM) recorded rod-shaped particles with an average width of 31.04 nm and length 137.51nm. X-Ray Diffractometer (XRD) showed a cubic spinel phase of γ-Fe₂O₃ (maghemite). Furthermore, SIONs exhibited good antibacterial activity against multidrug-resistant Helicobacter pylori. Our study demonstrated that the Minimum Inhibitory Concentration (MIC) of SIONs against multidrug resistant (MDR) H. pylori was 3.1 µg/ml. TEM image showed the cell rupture of H. pylori indicating fragmented cell membrane and leakage of bacterial components in those culture treated by SIONs. Cytotoxic activity test revealed that SIONs have no adverse effect on human epithelial cell line so it may be used safely as a natural product. The use of S. platensis as a nanofactory for the IONs synthesis could have a great role in the treatment of H. pylori infection in the future.