We have to study the factors affecting the synthesis of Co doping ZnO Nano powder with the sol – gel method to study the effect of quantity or doping concentration we fix the reaction base at pH = 9 and change the doping concentration the structural and morphology carried out with X-ray and SEM show hexagonal wurtzite nanoparticles for Zn 1-x Co x O for x = 0.01 and x = 0.05 and increase of the cell volume and lattice parameter with increase of x concentration ,the florescence spectroscopy at room temperature show peaks at ultraviolet for both concentration with read shift for x = 0.05. To study the effect of pH value we fix doping concentration at x = 0.05, SEM shows a spherical nanoparticle with size 38 – 52 nm for pH = 9 and hexagonal nanoparticles with size 42 – 52 nm for pH = 6. The florescence spectroscopy at room temperature exhibit that for pH = 9 there is no band observed in the ultraviolet region bands are around 380,420 and 475 nm. The Ultraviolet/Visible (UV) Spectroscopy exhibit decrease of the band gap energy with increase doping concentration and decrease with increase pH value. Copyright © VBRI Press.