The geological survey and laboratory work were carried out on the granitic rocks in southwestern Hokkaido for past several years by authours. Sixteen granitic rocks were newly analyzed chemically by them. The present paper deals with the chemical and mineralogical compositions of the granitic rocks in the relation with their occurrence. Most of granitic rocks in southwestern Hokkaido belong to granodiorite chemically and mineralogically.
The granitic rocks from the main zone including those of Imagae, KudoSetana, Kumaishi and Matsumae show the similar characteristics chemically and mineralogically. However those from Okushiri at the west side of main zone and from Shi-ôtaki, Kagenosawa and Kayanuma at the east side are different from those of the main zone in the chemical characteristics, although they can't be distinguished mineralogically from the granitic rocks of the main zone. It is significant that the granitic rocks of Shinôtaki, Kagenosawa and Kayanuma intruded in Miocene or far later than the others.