The structure and stability of rubidium ions (Rb + n ) are investigated experimentally from the relative mass abundance spectra. Rb + n clusters are produced in a liquid metal ion soruce. A sharp reduction in the relative abundances of cluster ions is observed at the edges of Rb + 3, Rb + 5, Rb + 9, Rb + 19, Rb + 21 and Rb + 31. In the region of n ⪢ 9, Rb + 13 shows a pronounced maximum. The relative abundances of certain sizes, Rb + 10 and Rb + 22, are very small. Some of the mass spectral features we observe are similar to those observed in the neutral alkali clusters. We also observed several new features: the large amplitude of Rb + 13 and a sharp reduction beyond Rb + 31. Certain features appear only in the cluster ions and not in the isoelectronic neutrals. Mass spectra of the neutral fragments generated by unimolecular decomposition of the cluster ions are also presented.