Nickel ferrite (NiFe₂O₄) nanoparticles were synthesized using the sol-gel auto combustion method, and the powdered samples were calcined at two temperatures, 100°C and 200°C. The structure of nickel ferrite nanoparticles was determined using X-ray diffraction (XRD) patterns. The nickel ferrite nanoparticle size was calculated using the Debye-Scherrer formula and was found to be 15.53 nm and 17.14 nm for 100 °Cand 200 °C. Field Emission Scanning Electron Microscopic (FESEM) analysis reveals that the samples exhibit spherical morphology with crystalline in nature and also show some agglomeration. The phase formation of nickel ferrite nanoparticles was further confirmed from the energy dispersive x-ray (EDAX) spectra which shows strong peaks for the existence of all the elements in it. The work investigates the magnetic properties of the samples and both the samples exhibit ferromagnetic behavior. The optical band gap obtained for the samples is 2.5 and 2.6 eV for N1 and N2 samples. The antimicrobial activity especially the anti-algal effect of NiFe₂O₄ nanoparticles on freshwater microalgae Chlorella pyrenoidosa in a dose-dependent manner is also reported.