Mechanochemical processing of anhydrous chloride precursors with Na2CO3 has been investigated as a means of manufacturing nanocrystalline SnO2 doped ZnO photocatalysts. High-energy milling and heat-treatment of a 0.1SnCl2+0.9ZnCl2+Na2CO3+4NaCl reactant mixture was found to result in the formation of a composite powder consisting of oxide grains embedded within a matrix of NaCl. Subsequent washing with deionized water resulted in removal of the NaCl matrix phase and partial hydration of the oxide reaction product with the consequent formation of ZnSn(OH)6. The extent of this hydration reaction was found to decrease in a linear fashion with the temperature of the post-milling heat-treatment over the range of 400–700 °C. For a heat-treatment temperature of 700 °C, the SnO2 doped ZnO powder was found to exhibit significantly higher photocatalytic activity than either single-phase SnO2 or ZnO powders that were synthesized using similar processing conditions. The heightened photocatalytic activity of the SnO2 doped ZnO was attributed to its higher specific surface area and the enhanced charge separation arising from the coupling of ZnO with SnO2.