With the increase of general knowledge and the advancement of science and technology, antibacterial substances were used more than antibiotics. In our current study, the antibacterial virtues of CFO/BiOI nanocomposite were investigated due to its high importance on Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Bacillus cereus. MIC, MBC , Disk Diffusion and IC50 tests Cefalotin (CF), Amoxicillin (AMX), Gentamicin (GM), Trimethoprim-sulphamethoxazole (SXT) and Ceftriaxone (CRO) antibiotics in concentration 30W, 10i, 10t , 25h and 30 were used to find the antibacterial properties of the synthesized nanocomposite, respectively. For the synthesis of nanocomposites polyethylene glycol (PEG) and sulfonic acid was used as a solvent. It is noteworthy that the synthesis was performed by heat dissolution method without the presence of surfactant. Also, various techniques such as X-Ray Diffraction(XRD), Scanning Electron Microscope (SEM), High resolution mapping and Energy Dispersive X-ray spectroscopy (EDAX) have been used to determine the properties of produced nanocomposites. SEM test results showed that the formed nanoparticles were globular and their size was limited area of 22 to 34 nm. The results showed CFO / BiOI nanocomposite exhibits strong significant biological activity against Bacillus cereus. The results of MBC (Minimum Bactericidal Concentration) and MIC (Minimum Inhibition Concentration) tests for CFO/BiOI nanocomposites on bacteria were examined in the range of 0.12-0.48 mg/ml and 0.06 to 0.24 mg/ml respectively. According to the results, the minimum IC50 value was determined at a concentration of 0.061 mg/ml. On the other hand, the most resisting and susceptible bacteria in this method were Pseudomonas aeruginosa and Bacillus cereus, respectively. These findings are identical to those of a prior study on CoFe2O4 nanoparticles antibacterial properties. MBC of the nanocomposites, 50 µl from all the tubes that showed no obvious bacterial growth were distributed on BHI agar plates and incubated for 24 h at 37 ◦C. The MBC endpoint is defined as the lowest concentration which killed 98% of the bacterial population.