Magnetic cores loaded with metallic nanoparticles can be promising nano-carriers for successful drug delivery at infectious sites. We report fabrication, characteristic analysis and in vitro antibacterial performance of nanocomposites comprising of cobalt cores (Co-cores) functionalized with varied concentration of silver nanoparticles (AgNPs). A two-step polyol process synchronized with transmetallation reduction method was used. Co-cores were synthesized by cobalt acetate and decoration of AgNPs was carried out by silver acetate. The density of AgNPs was varied by changing the amount of silver content as 0.01 g, 0.1g and 0.2 g in the synthesis solution. Both AgNPs and Co-cores were spherical in shape having size range of 30-80 nm and 200 nm to more than one micron respectively as determined by scanning electron microscopy. The metallic nature and face centred cubic crystalline phase of prepared nanocomposites were confirmed by x-ray diffraction. Biocompatibility analysis confirmed high cell viability of MCF7 at low concentrations of tested particles. The antibacterial performance of nanocomposites (Co@AgNPs) against Escherichia coli and Bacillus subtilis was found to be AgNPs density dependent and nanocomposites with the highest AgNPs density exhibited the maximum bactericidal efficacy. We therefore, propose Co@AgNPs as effective drug-containers for various biomedical applications.