Microwave combustion method (MCM) was used to synthesize of spinel Sr-NiFe2O4 NPs by employing the fuel Urea. The physical characteristics were obtained by following methods viz. powder XRD, SEM, EDX, FT-IR and VSM techniques. The diffraction studies revealed that the average crystallite size exist in the band of 15.22 nm to 25.55 nm. The HR-SEM pictures revealed the agglomerated and spherical morphology of spinel Sr-NiFe2O4 nanoparticles. Elemental analysis ensured that the existence of Ni, Sr, O and Fe ions. The broad peaks at 439 cm -1 and 585 cm-1 corresponds to octahedral metal stretching and tetrahedral metal stretching of Sr-NiFe2O4 respectively. Magnetic results revealed that the prepared NPs are ferromagnetic in nature. The antibacterial activity (ABA) of gram-positive Staphylococcus aureus, Bacillus subtilis have been investigated using Sr-NiFe2O4 NPs. It was found that the improved activity is intensified with smooth Sr2+ doping as it causes a decrease in the grain size.