The importance of specific sterols present in olive oil, as well as a-tocopherol and polyphenols, in the prevention of certain diseases is well known. Establishing differences in the content of these essential components on the EVOO (Extra Virgin Olive Oil) is important, and allows an evaluation of the quality and suitability of olive oil for health. In this chapter, the composition of fatty acids, sterols and polyphenols in most monovarietal oils of eastern Spain were analyzed, to quantify each of these constituents in the different varieties. This would allow suitable oils to be chosen for specific nutrition programs, or in preventive pharmacology. The specific composition of each component was obtained for each variety. The oils tested were produced in a pilot project using cold extraction, followed by centrifugation. The olives used were graded as 3-3.5 in ripeness under standard colorimetric scales, except the varieties from Blanqueta and Marfil, in which it was sought a similar ripeness time. Olives were obtained from selected trees from commerial groves, most of them several hundred years old. And some were classified as emblematic trees. Fatty acids have been studied using n-heptane extract to separate the fatty acid methyl esters with High Performance Liquid Chromatography (HPLC). Sterols, tocopherols and polyphenols were analyzed according to the procedures described by Sanchez-Casas, who modified the method produced by Slover [74]. Total phenolics were estimated according to the Folin-Ciocalteu spectrophotometric method [74]. All materials had been previously characterized by UPOV (International Union for the protectionof new Varieties of Plants) TG99/4.