Nickel (Ni) is the most recently discovered essential element for higher plants. It has been found that Ni deficiency depresses urease enzyme activity and other enzymes responsible for nitrate reduction and as a result, increases accumulation of urea, nitrate, and several amino acids in plant tissues. Urea is an important nitrogen fertilizer in today's agriculture and its suitability for field crops has been well evaluated. Urea is a widely used fertilizer because of its low costs, easy in handling and high nitrogen content. However, urea in comparison to nitrate is not a desirable N source for hydroponic grown plants. Our knowledge of the complete biological significance of nickel for plant productivity is still quite limited. However, with the demonstration of the essentiality of nickel in different plant species and the increased use of urea as a nitrogen source, the importance of understanding the chemistry and biology of nickel and its potential impact on agricultural production has never been greater. The impact of Ni nutrition on yield, quality, and nitrate content of leafy vegetables such as lettuce is still unknown. This work, therefore, was designed to study the impact of nickel nutrition and nitrogen source on lettuce yield and quality and accumulation of urea and nitrate in lettuce as one of the freshly consumed leafy vegetables. In this study, nitrogen was supplied with urea or nitrate ammonium at three concentrations (5, 10 and 20 mM). The lettuce plants were treatment by two nickel levels (0 and 0.04 µM in the form of NiCl 2 ). The plants were harvested 6 weeks after tralanting and the fresh weight of shoots and roots were determined. The shoot nitrate and urea concentrations, urease enzymatic activity in the leaves, shoot N, Fe and Zn contents and the membrane permeability of root cells were also measured. The results of this study indicated that Ni nutrition significantly promoted the growth of urea-fed plants although it had no significantly affect on the growth of nitrate-fed plants. In this study, the shoots and roots fresh weight of the urea-fed plants increased when nickel was supplemented. The shoot NO 3 -N concentrations in both nitrate-fed and urea-fed plants were significantly affected by the nickel nutrition. Nitrate concentration in the shoots of lettuce plants decreased significantly with nickel nutrition particularly of the high nitrogen levels (20 mM). Ni supplement increased the urease activity in the leaves significantly. The shoot concentrations of urea in the urea-fed plants without nickel supplement were relatively high in the absence of Ni while it decreased significantly Key Words: Nickel, Urea, Urease enzyme, Nitrate, Membrane permeability, Lettuce.