Nano-sized ZnO colloids were prepared by use of spray combustion method. for combustion reaction, $Zn(NO_3)_2{cdot}6H_2O$ and $CH_6N_4O$ were employed as an oxidizer and a fuel. Exothermic peak was shown at $230^{circ}C$ by DTA/TGA, and it was considered as a combustion reaction followed by ignition of the precursor mixture. In case of spray combustion method, because insufficient contents of molecules and radicals generated from precursor droplets may lead an incomplete igmition, the ignition temperature of combustion chamber was chosen at $500^{circ}C$. For diminishing aerosol coagulation, the droplet number concentration was reduced by filter media. The fluid was laminar with 2.5 seconds of aerosol residence time. The synthesized colloids had spherical shape with 180 nanometer size, and the crystalline phase was ZnO with hexagonal structure.