Abstract Lattice parameters, magnetic susceptibilities (over the temperature range 98–298°K) and reflectance spectra (uv and visible) of solid solutions of CoOZnO up to 10% M CoO have been studied. It is shown that true solid solution is achieved and that Co 2+ ions substitute the Zn 2+ ions in tetrahedral positions. The effect of addition of Co 2+ is to increase the a parameter and decrease the c a ratio. The magnetic moment of Co 2+ has been found to be 4.54 ± 0.05 μ B by extrapolation. A discussion of the structural and magnetic data in terms of the presence of a C 3 v effective symmetry is given.