Author Institution: Department of Chemistry, Faculty of Science, Shizuoka University,; Oya 836, Shizuoka, Japan; Center for Instrumental Analysis, Shizuoka University; Department of Chemistry, Faculty of Science, Shizuoka University,; Oya 836, Shizuoka, JapanThe rotational spectrum of MCN (M=Ag, Au) was observed by employing a source-modulation mi crowave spectrometer. The MCN species was generated in a dc glow discharge through the mixture of CH3​CN and Ar by a sputtering reaction with an metal target. The spectrum of MCN was observed in the ground and ν2​ vibrational excited states. The molecular constants derived from the observed transition frequencies were compared with values of theoretical calculations reported in literature