The Sultanate of Oman is considered to be a country that suffers from limited water resources. Surface water resources are scarce and groundwater is the main source for domestic, agricultural and industrial uses. Over-pumping and reservoir depletion due to water shortage led to seawater intrusion in coastal areas. Soil and ground water resources are becoming extremely saline and adequate resources of good quality irrigation water have become limited. Desalination and treated wastewater are among other alternatives which are currently used for domestic, irrigation, aquifer recharge, fish culture, cooling, construction and industrial purposes. Treated wastewater is the wastewater that has been subjected to one or more of the physical, chemical, and biological processes to reduce pollution and health hazards. Treated wastewater helps maintain environmental quality while providing sustainable agriculture and preserving scarce water sources. The numbers of wastewater treatment plants in Oman have been increased enormously. The produced water has a great opportunity to be utilized in forage production. Wide ranges of forage crops are cultivated in the Sultanate. Maize is one of the most important annual forage grass cultivated in Oman during winter and summer along with Sorghum. Flood irrigation is the most dominant irrigation system used in this type of cropping system. Field experiments were conducted during the 2006/07 season at Agricultural Research Center, Directorate General of Agricultural & Livestock Research in Rumais to determine the effect of water quality (tertiary treated wastewater and fresh water), water quantity (1.4ETC, 1.0ETc and 0.6ETc), and their interaction on the growth, yield and water use efficiency of forage maize. In addition, the chemical composition of forage maize plant that had been irrigated with treated wastewater was evaluated in comparison with those irrigated with fresh water. Soil moisture distributions and salinity redistributions were monitored through out the experiments. The results indicated that treated wastewater leached more salts down the profile than fresh water.. Treated wastewater also reduced the SAR by 74% whereas fresh water reduced it by 68%, but fresh water had a higher SAR to start with. The higher the quantity of water applied, the higher was the salinity and SAR reductions, Fresh water treatments were observed to have higher moisture content in comparison with the treated wastewater. This was attributed to the fact that treated wastewater contained dissolved organic matter that slightly improved the physical conditions of the soil which resulted in increased water penetrations, and contained higher amounts of nutrients that resulted in vigorous plants which abstracted more water. The results also indicated that plants irrigated with treated wastewater contained higher nitrogen concentrations at all levels of water quantities than those irrigated with fresh water. But K, P, Ca, Mg, Fe, S, B, Zn, Cu and Mn uptakes of forage maize did not show any significant differences between fresh and treated wastewater, Plants irrigated with treated wastewater had higher growth rates (in term of plant height) in comparison with those irrigated with fresh water. The number of leaves/plant, Leaf length and leaf area (cm2) did not show any significant differences among water types, water quantities or their interactions. Treated wastewater had shorter time for 50% male and female flowering of forage maize plants than fresh water, indicating earlier maturity. Plants irrigated with treated wastewater had higher chlorophyll content than those irrigated with fresh water for all levels of water applications. Treated wastewater gave higher average green forage yields (60.79 t/ha) and dry matter yields (11.57 t/ha) than fresh water which yielded 36.27 t/ha and 9.46 t/ha of green forage and dry matter respectively. Plants irrigated with treated wastewater were more efficient in using the water than those irrigated with fresh water for all water quantities. The highest water use efficiency (3.51 kg/m DM) was achieved with treated wastewater under the 1.0ETO water applications. This study concluded that treated wastewater irrigations increased yields of forage maize and their water use efficiency without significantly affecting any metal accumulations in the soil or plant leaves. Further economical studies and use as animal feed are recommended. .