This study introduces a novel way of using pyrolytic gas generated by the pyrolysis of waste high-density polyethylene (HDPE) for metal oxide reduction. A case study on NiO was carried out to reveal the feasibility of the method. Thermodynamic calculations were performed to guide and better understand the experiments. It was predicted that the pyrolytic gas mainly consisted of H-2, CH4, and C6H6. HDPE pyrolysis and NiO reduction were simultaneously carried out during heating to the temperatures 550-900K. NiO was reduced to Ni by the pyrolytic gas carried by Ar flow above 650K. The conversion of HDPE to the pyrolytic gas increased as the temperature increased to 900K. The extent of NiO reduction also increased with temperature due to enhanced HDPE pyrolysis. NiO reduction was completed at 900K. It is feasible to use waste HDPE to reduce metal oxides such as NiO.