The Middle Proterozoic pillow lavas distributing over Yuanqu, South- eastern Shanxi province, are composed of basalt-andesites and andesites, which have undergone, more or less, alkalfeldspathiztion, sericitization and chloriti- zation.The variationin composition from core to margin of the pillows, and to the groundmass was examined by chemical methods. At the core the Na2O content is the highest but it gradually decreases towards the margin; The Mg0 content in the pillows is lower than that in the groundmass. It was located that the Luliang-West Henan rift valley appeared as a shallow sea,while the lava flows emplaced.Two modeles of formation on the individual pillows can be recognized.The quenching temperature of the pillows is about 950℃.