This paper reported the synthesis,crystal structure and electrical conductivity properties of Ni-doped ZnO powders(i.e.Zn 1 X Ni X O binary system,X=0,0.0025,0.005,0.0075 and in the range 0.01≤X≤0.15).Iphase samples,which were indexed as single phase with a hexagonal(wurtzite) structure in the Zn 1 X Ni X O binary system,were determined by X-ray diffraction(XRD).The widest range of the I-phase was determined as 0≤X≤0.03 at 1200 C;above this range the mixed phase was observed.The impurity phase was determined as NiO when compared with standard XRD data,using the PDF program.We focused on single I-phase ZnO samples which were synthesized at 1200 C because of the widest range of solubility limit at this temperature.It was observed that the lattice parameters a and c of the I-phase decreased with Ni doping concentration.The morphology of the I-phase samples was analyzed with a scanning electron microscope.The electrical conductivity of the pure ZnO and single I-phase samples were studied by using the four-probe dc method at temperatures between 100 and 950 C in air atmosphere.The electrical conductivity values of pure ZnO and 3 mol% Ni-doped ZnO samples at 100 C were 2×10 6 and 4.8×10 6 1 ·cm 1,and at 950 C they were 1.8 and 3.6 1 ·cm 1,respectively.In other words,electrical conductivity increased with Ni doping concentration. This paper reported the synthesis, crystal structure and electrical conductivity properties of Ni-doped ZnO powders (ieZn 1 X Ni XO binary system, X = 0, 0.0025, 0.005, 0.0075 and in the range 0.01 ≦ X ≦ 0.15) , which were indexed as single phase with a hexagonal (wurtzite) structure in the Zn 1 X Ni XO binary system, were determined by X-ray diffraction (XRD). The widest range of the I-phase was determined as 0 ≦ X ≦ 0.03 at 1200 C; above this range the mixed phase was observed. The impurity phase was determined as NiO when compared with standard XRD data, using the PDF program. We focused on single I-phase ZnO samples which were synthesized at 1200 C because of the widest range of solubility limit at this temperature. It was observed that the lattice parameters a and c of the I-phase decreased with Ni doping concentration. The morphology of the I-phase samples was analyzed with a scanning electron microscope. The electrical conductivity of the pure ZnO and single I-phase samples were s tudied by using the four-probe dc method at temperatures between 100 and 950 C in air atmosphere. The electrical conductivity values ​​of pure ZnO and 3 mol% Ni-doped ZnO samples at 100 C were 2 × 10 6 and 4.8 × 10 6 1 · Cm 1, and at 950 C they were 1.8 and 3.6 1 · cm 1, respectively.In other words, electrical conductivity increased with Ni doping concentration.