Dopamine and ascorbic acid has been fractionally determined at nickel oxide nanoparticles (nanoNiO x) modified polycrystalline gold electrode (poly-Au), nano-NiOx/Au, with high selectivity using voltammetric techniques. Nano-NiOx/Au electrode, fabricated electrochemically, could resolve the overlapping obtained at the bare poly-Au electrode. Nano-NiOx/Au electrode was prepared by cycling of potential of Au electrode in diluted Watts bath in the potential range between 0.0 and –1.0 V vs. Ag/AgCl (KCl sat.), and was characterized morphologically and electrochemically. Effect of loading level of nickel was examined by changing the number of potential cycles for the deposition of nickel nanoparticles, i.e., 1, 2 and 5 potential cycles were used. Also the effects of the electrooxidation of the thus deposited nickel nanoparticles and pH of the electrolyte on the voltammetric behavior were investigated. The good calibration curve of an acceptable rectilinear range is obtained at nano-NiOx/Au electrode in which nano-Ni was prepared by two potential cycles and subsequently electro-oxidized in KOH solution.