Lithium and iron co-doped cadmium oxide Cd_0.9(Li_1-xFe_x)_0.1O (x = 0.1, 0.3, 0.5, 0.7) with NaCl structure has been synthesized using formate of the composition Cd_0.9(Li_1-xFe_x)_0.1(HCOO)₂·2H₂O as a precursor. The NMR spectroscopy results demonstrate that the structure of lithium-doped cadmium oxide appears to have impurity centers only of one type. All the synthesized samples show a metal-like conductivity as indicated by the growth of their electrical resistance with temperature increasing in the interval 78–330 K. The study of the magnetic properties of the Cd_0.9(Li_1-xFe_x)_0.1O samples at 5 and 300 K revealed that they are ferromagnets, whose saturation magnetization increases with the iron concentration both at low and room temperature reaching the maximal values in the samples with a Li and Fe concentration of 3 and 7 at.%, respectively. An enhancement of the iron concentration in Cd_0.9(Li_1-xFe_x)_0.1O from x = 0.5 to x = 0.7 leads to an abrupt growth of the magnetization from 0.30 to 1.94 emu/g at 5 K and from 0.16 to 1.03 emu/g at 300 K. Iron doping with a simultaneous reduction of the lithium concentration also results in an increase of the band gap. The properties of these compounds are explained on the basis of first-principles calculations of their band structure.