Tris(8-hydroxyquinoline) gallium(III) (GaQ(3))-Al2O3 core-shell nanowires with different shell thicknesses of Al2O3 coated on GaQ(3) nanowires were prepared by atomic layer deposition (ALD). The uncoated and coated nanowires exhibited similar photoluminescence (PL) spectra in the atmospheres of air, oxygen, argon, and water vapor at room temperature. The PL stability of the nanowires in these atmospheres was then examined for up to 4 h. Degradation of uncoated GaQ(3) nanowires in PL intensity with time was observed in air, oxygen, and water vapor. GaQ(3)-Al2O3 core-shell nanowires were only degraded in oxygen, but to a lesser degree than uncoated nanowires. Therefore, ALD of Al2O3 is effective in protecting the nanowires.