In this study, two green microalgae, Dunaliella bardawil and Chlorella ellipsoidea, were cultured in different concentrations of nitrogen as sodium nitrate. These concentrations were 0.0 (nitrogen-free), 2.5, 5.0, 10.0, 25.0 and 50.0 mM N in case of D. bardawil and 0.0, 0.25, 0.50, 1.00, 2.5, 5.0 and 10.0 mM N in case of C. ellipsoidea. The results revealed that dry weight, protein, carbohydrates, chlorophyll a and chlorophyll b of D. bardawil were highly reduced in N-deficient cultures, whereas carotenoids were unaffected. Glycerol production by Dunaliella decreased to about 25 % of control in the absence of nitrogen. Similarly, dry weight, protein and carbohydrate contents of C. ellipsoidea were greatly reduced in N-deficient culture, whereas chlorophyll a and chlorophyll b of the same alga seemed to be slightly affected by the absence of nitrogen. Supplementation of nitrogen caused an obvious increase in dry biomass gain and biochemical components of the two algae. D. bardawil grown in N-deficient culture produced massive amounts of β-carotene reached to about 227.2 % of control. On the other hand, the accumulation of β-carotene in Chlorella cells was unaffected by the absence of nitrate. The content of β-carotene significantly decreased in both microalgae at the higher doses of nitrate. The contents of vitamin E and vitamin C were greatly reduced in both microalgae grown in N-deficient cultures. Supplementation of nitrate caused an obvious increase in the contents of both vitamins in Dunaliella. Contrarily, In case of Chlorella, while vitamin E was not detected, the content of vitamin C was greatly reduced in all doses of nitrate.