This research, for the first time, report the synthesis of core-shell magnetic nanoparticles (NPs) consisting poly acrylic acid (PAA) coated cobalt ferrite (CF) using a simple co-precipitation route. Nanocrystalline PAA@CF-NPs, particle size of 9.4 nm, exhibited saturation magnetization as 28.9 emu/g, remnant magnetization as 8.37 emu/g, and coercivity as 543 Oe. Keeping biomedical applications into consideration, PAA@CF-NPs were further analysed to evaluate antimicrobial performance against Gram positive (Staphylococcus aureus and Bacillus subtilis) and Gram negative (Pseudomonas aeruginosa and Escherichia coli) bacteria, and biocompatibility with reference to activated splenic cells. The PAA@CF-NPs were viable to the normal splenic cells (up to 1000 μg/ml) and do not affect the ability of fast dividing ability of the cells (activated splenic cells). An optimized dose of PAA@CF-NPs was intramuscularly administrated (100 μg/ml) into Albino mice to evaluate acute toxicity. The results of these studies suggest that injected PAA@CF-NPs do not affect vital organs mainly including liver and kidneys that confirmed the heptic/renal biocompatibility. The outcomes of this research project such developed nano-system for biomedical applications, mainly for magnetically guided drug delivery and image guided therapies development. However, to support the proposed claims, extended in-vivo studies are required to explore bio-distribution, chronic toxicity, and homeostatic conditions.