Chaetoceros simplex Ostenfeld of marine diatoms was isolated and purified from the sub-surface waters of the north-western part of the Red Sea, Egypt (Hurgada). The isolated grown cells are exposed to different concentrations of nitrate and phosphate to estimate their effects on the growth and some metabolic activities of the organism. In general, the results indicated thatconcentrations of 100 μM nitrate and 5μM phosphate stimulated the algal growth by 60% and 32%, respectively in the 8 th day of culture. While, the values of 300 μM nitrate and 50 μM phosphate exhibited a decrease in the algal growth by 44% and 49%, respectively as compared with the control culture. The photosynthetic pigments (Chl-a, Chl-c and Carotenoids), total soluble proteins and carbohydrates of Chaetoceros simplex followed a similar pattern of change to that of growth in response to different treatments of nitrate and phosphate. While, the addition of different treatments of nitrate and phosphate to F/2 medium decreased the total lipids of C. simplex. Statistical analysis of the data indicated that 5 μM phosphates and 50 μM nitrates were the highly significant and most effective concentrations that positively affect most of different metabolic activities of Chaetoceros simplex . Thus, Chaetoceros simplex culture could be used as larval feed or other purposes cultured using 50 μM nitrate and 5μM phosphate .