Novel materials for biomedical applications are in critical need of time. In the present work, the antibacterial properties of Co_1-x Ni _x Mg _x Fe₂O₄ nanoparticles (NPs) are assessed by the disc diffusion method for the common pathogen, that is, Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria. Overnight grown bacterial cultures were individually lawn-cultured on nutrient agar plates. All samples of NP concentrations (2 mg/mL) were prepared in sterile water and dispensed by sonication. Sterile filter paper discs (1.0 mm) were saturated by the (doped CoFe₂O₄) NP solution and incubated at 37 ± 0.1 °C for 24 h. The NPs with a fine size of 30-70 nm of Co_1-x Ni _x Mg _x Fe₂O₄ were achieved using the sol-gel method by doping CoFe₂O₄ initially with Ni and codoping with Mg, and their properties were studied by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared techniques. According to the results, Co_0.5Ni_0.25Mg_0.25Fe₂O₄ NPs exhibited potent antibacterial activities against s. aureus having an inhibition zone of 6.5 mm and P. aeruginosa having an inhibition zone of 6 mm as that were examined. The result shows that the bacteriostatic properties of NPs are used for numerous applications such as hyperthermia, antibacterial treatments, and targeted drug delivery.