Aging mechanism of quicklime and application of aged lime in conservation of cultural relics were studied by means of scanning electron microscope(SEM）and Xray diffractometry. Results show that calcium hydroxide crystals undergo both substantial size reduction and clear morphological change to form acicular Ca(OH)2(50nm in diameter and 200nm in length）and platelike Ca(OH)2 (100200nm in size）crystals in the course of aging. Meanwhile, research results indicate that the nano size and high reactivity of aged lime particles prompt the improvement of the mechanical properties of sticky ricelime mortar and hydraulic conductivity of Ca(OH)2alcohol dispersions, which solves the problems of low dissolution and permeability associated with the use of Ca(OH)2 solutions. This study is expected to found the stone for application of aged lime in conservation of cultural relics.