We determined the 87Sr/S6Sr ratios of 53 late Cenozoic volcanic rocks collected in an area of 700km X 300km in southern Peru along the Central Andes volcanic arc. The measured B7Sr/86Sr ratios scatter largely, ranging from 0.7049 to 0.7082. The ratios roughly correlate with Si02 contents, suggesting that the source magma is contaminated by crustal materials during fractional crystallization process. The lowest value is obtained in a basaltic rock.Regional variation in 87Sr/86Sr ratios is observed. In the along-arc direction from northwest to south east, the ratios increase, reach the maximum value near Arequipa City and then decrease in accordance with the change of.descending mode of the Nazca plate. The maximum 87Sr/86Sr ratio is observed in the region where the simple subduction of the Nazca plate is being distorted.