Physical and chemical characteristics of ashes formed at burning oil shale at temperatures 500, 600, 700, 800, 900 and 1030 degrees C were studied. Standard procedures were used to determine both pozzolanic activity and binding parameters. The most suitable characteristics were provided with oil shale ash formed at 700 degrees C. Ashes (15 and 30%) were added to ordinary Portland cement. The optimum pozzolanic characteristics and performances were provided by the mixture containing 15% ashes. The mixes meet the corresponding Turkish standards, and therefore, this oil shale call be used as all admixture in Portland cement.