Due to the extremely low aw value of olive oil, it is uncommon as substrate for growth of microorganisms.Nevertheless, we found that yeasts are the predominant microorganisms which can be found growing in it.Olive oil is a typical product of the Mediterranean area and is well known for its high nutritional value.The extra virgin olive oil is obtained from the fruit of the olive tree (Olea europaea L.) solely by milling and cold-pressing of olive flesh.Yeasts as predominant microorganisms in olive oil have either a positive role by debittering of the olive oil or negative roles by causing undesired acidity due to their lipolytic activity and spoilage of olive fermentations by their pectinolytic activity [1].