The Matsumae plutonic complex occurs to the north of the Cape Shirakami, southwestern Hokkaido, Japan. It is composed of the following nine rock types; clinopyroxenite, hornblendite I, hornblendite II, granodiorite, monzogabbro, quartz monzodiorite, adamellite, aplite I and aplite II. On the basis of the field evidences, at least four stages of magmatic intrusion can be assumed. These four stages of intrusion are considered to have occurred at about the same depth, though the cumulates (clinopyroxenite, hornblendite I, and II) are inferred to have crystallized at some greater depth. Petrochemistry of the Matsumae plutonic rocks are characterized by high K2O content, which resembles to those of the Cretaceous alkalic rocks in the Kitakami Mountains. The Cretaceous plutonic bodies in the Northeast Japan are classified into two groups; one contains a considerable amount of gabbroic rocks associated with acidic rocks (Gb type), and the other is composed mainly of acidic rocks with or without a small amount of gabbroic rocks (Gr type). In the Gr type plutonic bodies, which are dominant in the Cretaceous plutonic bodies, alkali content slightly increases from east to west, nevertheless alkalic rocks are very rare. Whereas the Gb type plutonic rocks have a wide compositional range from non-alkalic to alkalic, and alkalic bodies are concentrated in western part of the Kitakami Mountains. This distribution and the lateral variation of alkali in the Gb type is discordant with that in the Gr type plutonic bodies.