Oscillatoria acutissima (cyanobacteria) and Scenedesmus obliquus (green alga) were cultured under nitrogen starvation conditions and evaluated for growth and some metabolic activities. Under nitrogen starvation condition pigments, protein, saponification values and lipase activity were decreased, while carbohydrate contents were increased for tested organisms. At the same time, iodine number increased in O. ocutissima, and decreased in S. obliquus. Infera red analysis showed reduction in the concentration of amino group in lipid materials of both organisms. However, GLC analysis cleared that nitrogen was significantly reduced in the lipid materials. The intra-cellular fatty acids of O. acutissima showed reduction in the total saturated fatty acids and increase in the total unsaturated acids, meanwhile S. obliquus recorded the opposite trend.