[en] Sericites occurring in Cretaceous-Paleogene granitoids were dated by K-Ar method at two localities in the Chugoku District. Pale green sericite (2Ml poly-type) from the well known sericite deposit in the Mitoya area, San'in province, gives 51 Ma, whereas white sericite (1Md poly-type) from minute vein at Takaya, San'yo province, is dated at 86 Ma. Each age is identical with that of the surrounding granitoids within the analytical error. The concordancy in the age may suggest the genetic link between post-magmatic fluid activity of the Cretaceous to Paleogene granitoids and the sericite formation. (author)