Abstract: Alternate bearing is one of the major cultural problems and economic drawbacks particularly in olive groves which is the main fruit tree crop in the Mediterranean area as well as southern Europe. Changes in hormone concentrations might be attributed to alternate bearing habit. Therefore, concentrations of Abscisic Acid (ABA), Indole Acetic Acid (IAA), Gibberellic Acid-like substances (GA) and Kinetin-like Cytokinin were determined and their relationship to flower bud formation was examined during “on” and “off” years. Results showed significant differences in IAA, ABA, GA3-like and Kinetin-like-Cytokinin between “on” and “off” cropping years in various tissues of olive trees. Relative balances between GA3-like and an ABA concentration in tissues might be a key regulator of floral development and alternate bearing. Olive growers are advised to do fruit thinning during “on” year crop to reduce the occurrence of this phenomena.