A water culture experiment was carried out on lupin plants, to study the influence of different nitrate and ammonium ratios on growth, nutrient uptake and photosynthesis process, in respect of chlorophyll content and carbonic anhydrase activity (CAA). Nitrogen was applied in five NO3 /NH4 ratios : (100 : 00 ), (75 : 25) ,(50 : 50 ), (25 : 75) and (00:100). Results revealed that both shoots and roots dry weights wwere significantly increased as the portion of NO3 in the growth medium increased. Also P and Mg concentrations in the shoots were increased with increasing NO3. While, K and Ca in the shoots and K in the roots were increased with increasing NH4 level. 75% of applied N in NH4 form caused a decrease in Zn and Cu concentrations in the shoots. In contrast, Fe increased and no specific trend was observed for Zn , Fe and Cu in the roots. P uptake by shoots was not significantly affected, while P uptake by roots was significantly affected. Highest K uptake in shoots and roots was observed when NO3 was the sole nitrogen source. Ca uptake by shoots and roots significantly increased when portion of NH4 increased. Zn, Fe and Cu uptake by roots were increased significantly, when NH4 portion increased. In addition, Zn and Cu uptake by shoots of lupin plants were increased significantly when plants were fed with nitrogen all in NO3 from. Chl. a and Chl. ( a + b) showed the highest value when NO3 was the sole source for nitrogen, except Chl b. which showed the maximum value when NO3 was only 25% from applied nitrogen. In addition, CAA was significantly increased when 100% NO3 was used in the growth root medium.