Abstract: The cobalt nanoparticles over γ-Al₂O₃ support were prepared via chemical reduction of CoCl₂·6H₂O using NaBH₄ with various values of pH in the range of 11.92-13.80. Synthesized catalysts were studied through X-ray diffraction (XRD), N₂ adsorption/desorption (BET), H₂-temperature programmed reduction (H₂-TPR), H₂-chemisorption, O₂ pulse titration and temperature programmed oxidation (TPO) methods. Obtained results exhibited the synthesis solution pH showed a significant influence on the activity and selectivity in partial oxidation of methane reaction. The methane conversion, CO selectivity and H₂ yield were enhanced by increasing of the synthesis solution pH. Compared to other catalysts, the catalyst that synthesized at pH of 13.80, showed a superior ability in syngas production with a H₂/CO ratio of near 2 and also a proper stability against deactivation during the partial oxidation of methane.