According to the average quantities of rainfall, Iraq's arable land is divided into three regions: rainfall, semi-rainfall and rain-fed. The total Iraq's regions are suffering from inefficient utilization of natural resources as a result of dis-maximization of agricultural production function. The northern region on Ninava and Duhok Governorates is part of the northern region of Iraq which is located in the ensured rainfall zone and the figures of per donum yield of cereal crops are somewhat

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... her than the Iraqi figures, however, they are still less than the required figures. The average quantities of rainfall are annually fluctuated and, thus, considered the major determinant for producing cereal crops especially wheat and barley. The situation implies that an extensive efforts should be concentrated on administrating resources in order to increase per donum yield of cereals. The main thrust of this research is to estimate the impacts of rainfall resource on producing wheat and barley in the region for the period 1992-2008. The library and historic data gathering has been used with the assistant of some administrative officials in the agricultural departments of the region. Production function analysis of different specifications are used to estimate the basic parameters in the agricultural sector of the region. The estimates are based on fitted the usual linear, semi-log, inverse semi-log and the double-log production function. The results revealed that the double-log function was the more convenient function in presenting some important conclusions. Increasing of one unit of rainfall will increase per donum yields of wheat and barley by 0.956 and 0.611 kg/donum respectively. The annual increase of per donum yields of wheat and barley were about 0.250 and 0.214 kg/donum. Wheat production is carried on in first stage, while barley production is carried on in the second stage of production function. An additional unit of rainfall is added about 0.523 kg of