It was generally accepted that the total elimination of chlorine is favorable to build active supportednano-gold catalysts if chlorine-containing precursors was used especially for the total oxidation of CO.Here a series of Au/NiOx catalysts were prepared with co-precipitation method by tracing the chlorineconcentration in the washing step and tested by the total oxidation of CO. It was revealed that Au/NiOxcatalysts prepared from aqueous solutions with 4–8 ppm chlorine can be active catalysts and the temper-ature for CO total oxidation was <0◦C. The catalytic activity dropped sharply if the chlorine concentrationwas <4 ppm or >8 ppm. The catalysts were characterized by XRD, XPS, BET, TEM, HAADF-STEM and EXAFS,and the catalyst structures were explored. The different structures of the catalysts should be responsiblefor the activity variation and it was caused by the washing operation or the presence of different amountsof chlorine. Although active Au/NiOx catalysts can be obtained by tracing chlorine concentration, the roleof chlorine in the fabrication of active nano-gold catalyst was still unclear.