Abstract: THE OXYGEN ISOTOPIC EFFECT OF CRYSTALLINE WATER IN NATURAL CARNALLITE（KMgCl_3·6H_2O）Xiao Yun（Departmeut of Oceanography,Xiamen University,361005）ABSTRACT The oxygen isotopic composition of crystal water in natural carnallite is determined by a guani-dine hydrochloride method for the preparation of samples．The variation of oxygen isotopic composi-tions for the crystal water with different released temperature is observed．The results show that the~(18)O is preferentially enriched in the released crystal water at high temperature. Key words oxygen isotope carnallite crystalline water isotopic effect