The suitability of treated industrial effluent came from Al-Husseun Bin Abdullah II Industrial Estate (HUIE) wastewater Treatment Plant for irrigation of olive (Olea europaea L.) was during two complete vegetative cycles. The plants were nonbearing transplants under controlled conditions and bearing trees grown in the field. Irrigation with six electrical conductivities (EC = 0.78, 1.0, 2.0, 3.0, 4.0 and 5.0 dS m(-1),, respectively T-0, T-1, T-2, T-3, T-4, T-5) were compared in the greenhouse experiment. The olive trees under field conditions were 3, 4 5) trickle irrigated with treated effluent or potable water. Regardless of the cultivar, length and number of new shoots, diameter of the main trunk, leaf area and dry weight of the plants significantly enhanced under the influence of different treatments. A considerable variation in. the studied cultivars was noticed. 'Improved Nabali' was the most positively affective one. The leaf biochemical contents from proline and total chlorophyll contents showed no variations among the treated effluent treatments and studied cultivars. Proline content was enhanced by irrigation with treated effluent only under the field condition. Olive oil acidity and peroxide value were not affected by treatments. These results indicate that this kind of effluent is suitable for application to olive orchards under irrigation with continuous monitoring of mineral levels.