CoxZn1–xGa2O4 (0 ≤ x ≤ 1) nanoparticles were synthesized by the sol-gel method and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), 71Ga solid-state NMR spectroscopy, and UV/Vis spectroscopy. The results show that the CoxZn1–xGa2O4 nanoparticles were successfully obtained when the annealing temperature was 500 °C or above. The crystallite size of the as-prepared particles was 20–55 nm, and increased with increasing annealing temperature and decreasing x value. Zn2+ and Ga3+ ions were located in both the tetrahedral and octahedral sites in CoxZn1–xGa2O4 nanoparticles, and the inversion parameter (two times the fraction of Ga3+ ions in tetrahedral sites) decreased with increasing annealing temperature and increased with cobalt enrichment. The absorption spectra indicate that Co2+ ions are located in the tetrahedral sites as well as in the octahedral sites in the nanoparticles. The fraction of octahedral Co2+ ions decreased with increasing annealing temperature.