Soil acidification, which is known to be one of the reasons of forest decline, is associated with decreases exchangeable Ca and increases in Al concentration, leading to low Ca/Al ratio in soil solution. As tree rings are datable archives of environmental changes, Ca/Al ratios of annual growth ring may show deceasing pattern in accordance with the progress of soil acidification. This study was conducted to investigate Ca/Al pattern of Pinus densiflora tree ring in relation with the changed exchangeable Ca/Al ratios of soils with the progress of soil acidification. Three P. densiflora tree disks were collected from P. densiflora forests in Jeonnam province, and soil samples (0-10, 10-20, and 20-30 cm in depth) were also collected from the tree locations. Soils were analyzed for pH, exchangeable Ca and Al concentrations, and Ca/Al was calculated. Annual growth rings formed between 1969 and 2007 were separated and analyzed for Ca/Al. Soil Ca/Al was positively (P＜0.01) correlated with soil pH, reflecting changed soil chemistry due to soil acidification. The Ca/Al of tree rings also showed a decreasing pattern from 18.2 to 5.5 during the period, and this seemed to reflect historical acidification of the soils. Our results suggest that Ca/Al of tree ring is likely to be affected by exchangeable Ca/Al ratio of the soils and thus it needs to be considered as a proxy of the progress of soil acidification in P. densiflora forest in southern Korea.