The concentration and composition of the biopolymeric particulate organic carbon (BPC) of the major phytoplankton components (proteins, carbohydrates and lipids) were measured in the two Nile Rayahs El Tawfiki and El Menoufy. BPC along El Rayah El Tawfiki (4.32-18.59 mgC/l) was associated to the high extent of the biopolymeric C of proteins (4.73-18.36 mgC/l). While the biopolymeric C of carbohydrates ranged between 0.08 to 0.27 mgC/l. The total concentration of biopolymeric C at El Rayah El Menoufy ranged from 6.19 to 15.42 mgC/l. The maximum concentrations of BPC detected at some sites of El Rayah El Menoufy were related to the higher biopolymeric carbon in both proteins and lipids. The present results showed a maximum positive correlation between both carbonate and bicarbonate of water body of El Rayah El Tawfiki and El Rayah El Menofy and BPC of phytoplankton (r= 0.9 and 1). BPC of phytoplankton was strongly related to the fraction of biopolymeric C associated with phytoproteins (r= 0.79). Variations in the estimated biochemical components of phytoplankton at the investigated Nile Rayahs followed the trend: Proteins˃ carbohydrates˃ lipids which indicated the highest protein contribution to C-BPC in both studied areas. Lipids/carbohydrates ratio in the two studied regions ranged between 0.55 and 0.57, which showed high nutritional value of organic matter in phytoplankton. Whereas, proteins/carbohydrates ratio ranged from 39.88 to 43.82, which indicated the aging of organic matter in phytoplankton. El Rayah El Tawfiki recorded higher energetic value (127.86 Kcal/l) than El Rayah El Menoufy (124.45 Kcal/l).This study demonstrated that fluctuation in phytoplankton composition due to the changes in carbonate and bicarbonate concentrations will have more impact on nutritional quality and biopolymeric carbon (BPC) of phytoplankton.