The precursors with a low manganese content ≤ 0.07% Mn were synthesized by spontaneous crystallization from Zn2+, Mn2+ and C2O42−-containing solutions. The initial ratio Zn2+:C2O42− = 1:1 and 1:2 influences the morphology and prevailing orientations of the crystallites in the oxalate samples. The presence of such small Mn content in the samples does not change the morphology or size of the crystals. The ZnO and Mn/ZnO oxides with manganese content from 0.51×10−2 to 15.1×10−2 Wt % are obtained after thermal decomposition of the oxalates. The oxides preserved the morphology of the precursors. The catalytic tests show that the pure ZnO has a poor activity for CO oxidation reaction. Its doping with Mn promotes the catalytic activity (up from twice to five times) in spite of the very low contents of the dopants. The observed increase of the activity depends on both dopant concentration and Zn2+:C2O42− ratio, probably due to the different mechanism of the manganese inclusion and different morphology of the oxides. The catalysts of the 1:2 series are more active in CO oxidation reaction.