The Miyazaki Group consists of the Tano, Aya, Tsuma, Sadowara and Takanabe Formations in ascending order and is composed of conglomerate and sandstone in the lowest part and siltstone to mudstone in the lower to upper part. The greater part of the group yields abundant, well-preserved molluscan fossils and calcareous microfossils. Calcareous nannoplankton biostratigraphy was clarified on the Miyazaki Group developing in the northwestern hilly land of Miyazaki City. The Miyazaki Group extends from Late Miocene to earliest Pleistocene in age, and its age assignment agrees well with the planktonic foraminiferal biostratigraphy. The lower part of the Miyazaki Group is characterized by the joint occurrence of Reticulofenestra pseudoumbilica and Sphenolithus abies. Pseudoemiliania lacunosa appears in the lower part of the Sadowara Formation and coexists with R. pseudoumbilica and S. abies. In the upper part of the Takanabe Formation, planktonic foraminifer Globorotalia truncatulinoides and calcareous nannoplankton Gephyrocapsa oceanica appear in the lower stratum, and Discoaster brouweri becomes extinct just under the upper stratum of the G. oceanica zone. Therefore, the Pliocene-Pleistocene boundary is expected in this vicinity. Based on the occurrence of G. oceanica, the Pleistocene in the Miyazaki Group would be limited to the lowest part of the Pleistocene.