Novel all-inorganic Sb-based lead-free double perovskite Cs2AgSbX6 (X = Cl, Br or I) quantum dots exhibiting excellent air stability and strong blue emission with photoluminescence quantum yields of 31.33% were synthesized for the first time using a surfactant-assisted method. The ligand, oleic acid, could control the crystallization of the pure perovskite phase and significantly passivate the surface.