Effects of nitrogen sources (NO3--Nand NEL4+N- and urea-N) and different concentrations (882, 441, 1323 and 1764 mu mol/L-1) on growth and biochemical composition of Nannochloropsis oculata were tested. The algae grown in both 882 and 441 mu mol/L concentrations of NO3--N in the medium showed maximum cell numbers of 51.76 +/- 3.10x10(6) cells/ml and 26.38 +/- 3.07x10(6) cells/ml, respectively. On the other hand, NO3- concentration in the medium was increased 1323 mu mol/L and 1764 mu mol/L, maximum cell numbers were significantly increased 93.51 +/- 3.62x10(6) cells/ml and 112.29 +/- 11.64x10(6) cells/ml, respectively. The highest EPA content and total w-3 of fatty acids of alga were 29.83 +/- 1.50% and 38.00 +/- 1.86 % of the dry weight when NO3-N concentration was 882 mu mol/L, respectively. Total carotenoid content of 882 mon in the concentration of N represented the highest value in the N. oculata biomass. With NO3-N concentration at 1764 mu mol/L, the highest value for chlorophyll a was 12.04 +/- 0.92 mu g/ml. As a result, nutrient limitation severely reduced cellular growth rate, on the other hand, cellular growth rate increased by more nitrogen concentration. Biochemical composition, particularly EPA values, changed in accordance with not only NO3- -N, NH4+-N and Urea-N concentrations but also harvest time.