The fossilized olive leaves were found in the Aegean island, Santorini, south of its capital, Fira. From recent studies, they are dated round 50.000 - 60.000 years old (Friedrich W.L. et Velitzelos E., 1986). They have been fossilized through the process of carbonisation that is the stamping of their original substances from carbon between volcanic tuffs. As far as the condition of the fossilized leaves and the surrounding stone is concerned, the direct environment (with data from the National Institute of Environmental Data) and physicochemical analysis that determine the degree of corrosion were studied. As far as the structure of the fossilized leaves and the surrounding stone is concerned, physicochemical analysis of the quality and quantity of elements and minerals were held. The stages of conservation were chosen according to these studies and include cleaning and removal of soluble salts with the use of compresses of neutral paper or absorbent clay (sepiolite). Concerning the removal of insoluble salts, mechanical methods of cleaning were used. For the consolidation of the fossils we used low concentration solutions of silicate esters and for their final protection low concentration solutions of silicate resins, because of the compatibility of these materials with the siliceous fossilized materials.