Background and Objective: Due to the increased prevalence of microbial resistance against chemical antimicrobial agents, the biological effects of metallic nanoparticles have recently been studied by researchers. In this regard, the present study aimed to investigate the antimicrobial effects of iron oxide nanoparticles made by chemical methods in different concentrations on bacteria isolated from urinary tract infections. Materials and Methods: In this descriptive cross-sectional research, iron oxide nanoparticles were synthesized by chemical precipitation method using chemical reactants and only by controlling the conditions and applying optimal conditions. Subsequently, their bactericidal effects on the six common bacteria causing urinary tract infections was studied using agar well diffusion method. The minimum inhibitory and bactericidal concentrations of nanoparticles were determined as well. In addition, the antibiotic resistance pattern of bacteria was investigated for antibiotics Gentamycin, amikacin, ampicillin, nalidixic acid, ciprofloxacin, norfloxacin, sulfamethoxazole using disk diffusion method. Results: The iron oxide nanoparticle was made in a spherical shape with a diameter of approximately 60 nm. Bacteria had an extensive antibiotic resistance, but iron nanoparticles were effective on all 6 bacteria, and the minimum inhibitory and bactericidal concentration to Proteus mirabilis, Klebsiella pneumoniae, staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Serratia marcescens were 0.32, 0.04, 0.02, 0.08, 0.04, and 0.02 at 1.25, 0.08, 0.61, 32 0, 16.0, and 16.0 mg/mL respectively. Conclusion: Iron oxide nanoparticles showed a wide spectrum of effects at very low concentrations against bacteria, and these nanoparticles could be considered as an appropriate candidate for the treatment of bacterial infections after extensive research.