Abstract: During the last 15 years, many olive cultivars have been introduced in the Kingdom of Saudi Arabia without any study on their biological and physiological behaviour and characteristics. This work aimed to determine the floral biology and the reproductive behaviour of five olive cultivars planted in Al-Jouf region and to choose the right cultivars adapted to the agro-ecological conditions of KSA. For each cultivar, floral biology in relation to phenological stages and flower quality and fertility behaviour under self and free pollination were determined for each cultivar. Notable significant differences between the cultivars were observed in all characteristics considered. Among the productive characters, all the olive cultivars showed a good productive behaviour with particular interest for ‘Picual’ and ‘Sourani’ cultivars. Regarding pollen characteristics, ‘Sourani’ and ‘Picholine’ reflected better pollen quality while the evaluation of flower quality and bloom showed good performance in all cultivars except for ‘Zaiti’ and ‘Nabali’ cultivars. In all cultivars, a positive response to open pollination was significantly consistent when compared with self pollination. The self-incompatibility index ISI was higher than 0.5 for all cultivars classified them as partially self incompatible cultivars. These results suggest that the five olive cultivars performed well in Al-Jouf conditions with a high phenological variability between cultivars for the parameters evaluated.