Abstract: The level of delta-7-stigmastenol (D-7-stigmastenol) contained in olive oil is a new criterion for oil quality, particularly its purity from adulteration with other seed oils. In this study, 79 olive samples were collected and analyzed from different areas of Palestine to study the factors affecting D-7-stigmastenol levels in the oil. These areas included the provinces of Jericho, Hebron, Bethlehem, Ramallah, Salfeet, Nablus, Jenin, Tulkarem and Qalqilyah. The study began in October 2007 and ended in July 2008. The following 11 factors were taken into consideration during sample collection: olive fly infection, topography, olive storage before pressing, geographical area, effect of olive seeds during oil extraction, effect of pressing temperature, presence of olive leaves during oil extraction, soil type, maturity index of the olive fruit, olive variety and oil preservation and storage in terms of storage container types. The results show that soil type, region, maturity index and olive fly infection are the main factors affecting D-7-stigmastenol. Pressing temperature, olive storage before pressing, olive variety and oil storage showed a moderate effect. Olive seeds, topography and presence of olive leaves had a negligible effect on D-7-stigmastenol levels in the oil.