The (KI)(n)(-) (n = 1-4) and K(KI)(n)(-) (n = 1-3) clusters were studied by negative ion photoelectron spectroscopy and ab initio calculations. Comparison between the theoretical vertical detachment energies and the experimental values revealed that multiple isomers may coexist in the experiments. The existence of two isomers for K(KI)(-) and K(KI)(2)(-) were confirmed directly by isomer-depletion experiments, in which the low adiabatic detachment energy isomers were depleted by a 1064 nm laser beam before the anions were photodetached by a 532 nm laser beam. Our results show that the most stable structures of the K(KI)(-), (KI)(2)(-), and K(KI)(2)-anions are chain structures, while those of their neutral counterparts are planar. Threedimensional structures start to appear at n = 3 for (KI)(n)(-/0) and K(KI)(n)(-/0). In the K(KI)n(-) cluster anions, the excess electron is localized on the extra K atom and forms an electron pair with the existing s electron of the K atom; the resulting negatively charged K prefers to interact with the other positively charged K atoms rather than with the I atoms. Both the anionic and neutral (KI)(4) clusters have cuboid structures, which may be regarded as the smallest structural motif of KI crystal.