Ni-doped SnO2 powders were prepared by the solvethermal method. The morphology, structure and elemental composition of Ni-doped SnO2 were characterized by TEM, EDAX, XRD, Raman and XPS. Gas sensing properties of Ni-doped SnO2 were also investigated by sensitivity measurements. The results show that Ni doping inhibits the grain growth of SnO2 and decreases the grain size, thus enhancing the gas sensitivity of SnO2. Oxygen vacancies formed by the substitution of Ni2+ for Sn4+ in the SnO2 matrix improves the gas sensing performance at low level of Ni doping. However, when Ni concentration reaches 30 wt%, the addition of Ni to SnO2 decreases gas sensitivity, which is attributed to the counteraction of the n- and p-type sensors