Green synthesis of nickel oxide nanoparticles (NiO NPs) using Physalis angulata leaf extract (PALE) as weak base sources and stabilizing agents has been reported. Chemical bonding and vibration spectroscopy, crystallographic structure, optical band gap, particle size and microscopic studies of NiO NPs were also investigated. Ni-O vibration modes of NiO NPs were analyzed by FTIR and Raman instrument at ~400 and ~900 cm-1wavenumber. XRD pattern of NiO NPs confirmed cubic crystal structure with space group Fm-3m. Optical band gap of NiO NPs determined by using Tauc plot method was about 3.42 eV. Particle size analyzer showed size distribution of NiO NPs was 64.13 nm which confirm NiO formed in nano-scale. Electron microscopic studies of NiO NPs were observed by using scanning electron microscopy and transmission electron microscopy.