The Sanbagawa metamorphic terrain of the Yawatahama district in western Shikoku is divided into three zones (I, II and II') on the basis of systematic variation of rock-forming minerals.Zone I: This comprises the area of Paleozoic and also Mesozoic formations. Zone I is characterized by the occurrence of prehnite and pumpellyite. But actinolite is rarely observed. This zone is corresponds to the prehnite-pumpellyite metagreywacke facies.Zone II: Prehnite and pumpellyite are not stable. The common minerals of basic rocks are glaucophane, actinolite, epidote, chlorite, white mica, albite and quartz. The physical conditions of this zone are intermediate between those of the glaucophane schist and greenschist facies.Zone II': The hornblende-oligoclase assemblage is characteristic of zone II'. Garnet and/or clinopyroxene are often associated with hornblende. This zone is restricted the area where the Kawamai tectonic mass is exposed. Probably zone II' is correlated to the epidote amphibolite facies. The meatamorphism of zones I, II and II' is progressive one, and then the metamorphic grade increases northwards. The retrogressive metamorphism, however, is observed in zone II'. In many basic rocks of zone II' the primary metamorphic constitures are replaced by chlorite, actinolite, glaucophane and epidote. The retrogressive metamorphism would have been caused by the change of the physical conditions owing to the upheaval movement of the Kawamai mass. It seems that the Sanbagawa metamorphism continued in the Lower Cretaceous age in the Yawatahama district.