Thermochemical stablities of the cluster ions composed of mixed rare gases were measured using a pulsed-electron beam high pressure mass spectrometer. The formation of trimer ion cores, i.e., A(+)(B)(2) and A(2)(+)(B)(1), was found when A and B are next to each other in the Periodic Table. This trend is similar to that for the pure rare gas cluster ions, i.e., the formation of ion core Rg(3)(+) for Rg = He, Ne, Ar, Kr, and Xe. Although Ar and Xe are not next to each other in the Periodic Table, the formation of the trimer ion core is found for Xe+(Ar)(2). This may be due to the fact that the ionization potentials of Ar and Xe are close to each other. The bond energies of larger cluster ions A(+)(B)(2)(B)(n-2) and A(2)(+)(B)(1)(B)(n-1) were found to be similar to those of homogenous cluster ions (B)(3)(+)(B)(n-3). The experimental bond energies were confirmed by ab initio calcuations with a modified G2(MP2) method [e.g., 0.2 kcal/mol (expt) and 0.3 kcal/mol (theory) for Ar-2(+).He].