The modifications in the microstructure and optical properties of cobalt doped nickel oxide nanoparticles (Ni1-xCoxO, x = 0, 0.01, 0.03, 0.05 and 0.10) synthesized by co-precipitation method is reported here. X-ray diffraction, field emission electron microscope, energy dispersive X-ray spectroscopy, and high resolution transmission electron microscopy techniques reveal successful incorporation of Co into the NiO lattice without compromising its intrinsic structure. X-ray photoelectron spectroscopy analysis confirms the compositional purity of the sample. The bandgap tuning of NiO is achieved by Co doping as confirmed by UV-visible absorption studies. Significant variation is observed in the luminescence intensity with Co doping. Surface oxygen vacancies and defects play a pivotal role in controlling the emission properties of NiO. This is the first report on the enhancement of PL intensity with Co doping of NiO nanoparticles. The modified spectral response of Co doped NiO is expected to have various optoelectronic applications.