Infrared transmission, electron spin resonance, and x‐ray diffraction measurements show unambiguously that RbC60and KC60are stable in air, in contrast to Rb6C60which decomposes rapidly upon exposure. The specimens studied transform to pure C60and other by‐products when heated above 100 °C, approximately the temperature of the orthorhombic‐fcc phase transition. The stability of these compounds raises the possibility of applying them as protective layers for the superconducting fullerides. ©1995 American Institute of Physics.