Abstract: Analysis of the diatomaceous earth collected from the Miocene type section in the Shanwang Basin of Shandong shows that the diatom assemblage there contains 16 genera, 95 species and varieties (of which 3 being new species), This fairly typical Miocene diatom assemblage may be correlated with the Miocene assemblage in Yakima district and Otis basin of Oregon, U.S.A. and those in W. Siberia, USSR. It is proved from the characteristics of the present diatom assemblage that the palaeoeeologieal environment during the diatom deposition was typically fresh lacus- trine facies, and the original lake surface was fairly extensive and the lake water was comparatively stable, but not very deep. The diatom assemblage contains species living now in more northern water bodies. This may be further proved by the associated grown cysts of Chrysophyta. The thin-bedded papery diatomaceous earth may be contributed partly to the fall of volcanic ashes, but most probably it is closely related to the seasonal palaeoclimatic changes as reflected in the growth repreduction stages of the diatoms.