The Mikame ultramafic body, located in westernmost central Shikoku, Japan, forms a nappe accompanied by the Maana Formation and low– to medium–pressure Oshima metamorphic rocks. This body is divided into the Shigiyama and Korotokibana masses. The Shigiyama mass is composed of very fresh dunite, wehrlite and pyroxenite; whereas the Korotokibana mass is composed of antigorite–bearing meta–serpentinite derived from dunite and wehrlite. Estimated equilibrium temperatures are 600–700 °C for the Shigiyama mass and 400–500 °C for the Kototokibana mass, respectively. The geological and petrological characteristics of the Mikame ultramafic rocks are similar to those of the Higo belt in central Kyushu, rather than those of the Mikabu and Kurosegawa belts, and the Mikame body is possibly equivalent to the Higo belt. The Shigiyama ultramafic rocks are subdivided into Mg– and Fe–rich suites based on their olivine and chromian spinel compositions. The Mg–rich suite is characterized by magnesian olivines (Fo_84–92) and high–Cr# [= Cr/(Cr + Al) = 0.5–0.8] spinels. On the other hand, the Fe–rich suite contains less magnesian olivines (Fo_74–88) and low–Cr# (= 0.3–0.4) spinels. The Mg– and Fe–rich suites of the Shigiyama ultramafic rocks are cumulates formed from depleted and less depleted magmas, respectively. The chemistry of the chromian spinels in the Mikame ultramafic rocks indicates that they formed by crystal accumulation from magmas generated in an arc setting. The Korotokibana meta–serpentinites resemble those from the Mariana forearc regarding their mineral assemblage, and olivine and chromian spinel compositions. The Korotokibana meta–serpentinites experienced dehydration at 400–500 °C, after serpentinization caused by addition of H₂O released from a subducting slab, whereas the Shigiyama ultramafic rocks contain no evidence for dehydration. The Mikame ultramafic body may have been the lower forearc crust produced by magmas with various degrees of depletion, later subjected to diverse hydration and dehydration processes.