The combination of matrix isolation infrared spectroscopic and quantum chemical calculation results provide strong evidence that scandium and yttrium monoxide cations, ScO+ and YO+, coordinate multiple noble gas atoms in forming noble gas complexes. The results showed that ScO+ coordinates five Ar, Kr, or Xe atoms, and YO+ coordinates six Ar or Kr and five Xe atoms in solid noble gas matrixes. Hence, the ScO+ and YO+ cations trapped in solid noble gas matrixes should be regarded as the [ScO(Ng)(5)](+) (Ng = Ar, Kr, or Xe), [YO(Ng)(6)](+) (Ng = Ar or Kr) or [YO(Xe)(5)](+) Complexes. Experiments with dilute krypton or xenon in argon or krypton in xenon produced new IR bands, which are due to the stepwise formation of the [ScO(Ar)(5-n)(Kr)(n)](+), [ScO(Kr)(5-n)(Xe)(n)](+) (n = 1-5), [YO(Ar)(6-n)(Kr)(n)](+) (n = 1-6), and [YO(Ar)(6-n)(Xe)(n)](+) (n = 1-4) complexes.