Synkinematic mineral separates from high-grade metamorphic rocks, which were collected from the Day Nui Con VoiRed River shear zone and the pre-Mesozoic metamorphic belt south of it, the Da NangKhe Sanh shear zone, and the Kontum massif in Vietnam, were dated by KAr method. Twenty-four analyses of hornblende, bioitite, and muscovite are clustered into four different groups: Early Proterozoic (ca. 17002000 Ma), Early Triassic (ca. 240258 Ma), Early Cretaceous (115116 Ma), and Late OligoceneEarly Miocene (2429 Ma). The KAr age data in general indicate cooling ages of ductile deformations and metamorphisms in Vietnam, suggesting an overprinting of thermotectonic events in Indochina from Early Proterozoic to Tertiary, which are generally consistent with tectonostratigraphic episodes in the region. The data demonstrate that the Indosinian orogeny in Vietnam has occurred during Earliest Triassic times, and Paleozoic orogeny (Caledonian and/or Hercynian) was not inferred by these KAr age data.