NiO cellulose nanocomposite (NiO-CN) were synthesized by the precipitation method and characterized by X-Ray diffraction (XRD), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDX) analysis, Fourier transform infrared (FTIR) measurements and UV–vis spectroscopy. The particles obtained have an average size of 20-30 nm as shown by TEM analysis. Fourier transform infrared (FTIR) measurements were carried out to identify the possible biomolecules responsible for the capping and stabilization of the nickel oxide nanoparticles synthesized by milk. The presence of elements in the nanoparticles was also analysed by Energy Dispersive X-ray (EDX) analysis. The results of EDX analysis show the weight percentages of C, O, Ni, and N-elements in the synthesized material were 41.65%, 52.49%, 3.81%, and 2.06%, respectively. Scanning Electron Microscope (SEM) has been used to assess the morphology of the nanoparticle. The effects of NiO-cellulose nanocomposite are screened for biological activities like, antibacterial activity was done by the Disc diffusion method. The bacterial organisms used in this study were Bacillus subtilis, Salmonela abony, Staphylococcus aureus and Escherichia coli. The observed inhibition zone for these microorganisms was found to be a minimum of 3.0 mm and a maximum of 22.0 mm. Moreover, This NiO-CN also decreases the 50% load of Leishmania donovani via MTT assay with 25µg/ml concentration after 72 hours incubation.