Diatoms of the Miocene Wajima and Tsukada formations distributed in Wajima City (Noto Peninsula, Ishikawa Prefecture) were examined. Non-marine lacustrine diatoms are found in the uppermost part of the Wajima Formation. The Tsukada Formation contains middle Miocene diatom assemblages which can be placed between the biohorizons D53 (12.3 Ma) and D54 (11.6 Ma) of the Denticulopsis praedimorpha Zone (NPD5B). An unconformity at the base of the Tsukada Formation ranging from ca. 16 Ma to 12.3 Ma indicates that a land area might be present in the western part of Noto Peninsula during the early Middle Miocene.