NiO-doped WO3 thick films were prepared by the screen-pfinting technique. The microstructure and the electrical properties were investigated as functions of the amount of NiO, partial pressure of oxygen, concentration of NO2 and temperature, The grain growth is inhibited by the addition of NiO. The electrical conductance of undoped WO3 is high at low partial pressure of oxygen. The electrical conductance of NiO-doped WO3 in air increases with NiO content of up to 1.0 mol%, and then it decreases. The sensitivity for NO2 gas increases for samples with 1.0 mol% of NiO, and then it decreases for 10 mol% NiO samples.