The marine diatoms such as Amphiprora gigantea O'Meara, Amphora coffeaeformis (Agardh) Kütz., Cocconeis heteroidea Hantz and Cyclotella meneghiniana Kütz. isolated from the coastal waters were made axenic and investigated for their growth, kinetics of phosphate uptake and assimilation. Phosphate-phosphorus at higher concentration depressed growth and division rates of all the diatoms. The uptake and assimilation of phosphate-phosphorus followed the classic Michaelis-Menten kinetics. Dark uptake was 37-71% when compared to light saturated uptake. Amphiprora gigantean, the largest diatom showed the low Ks and Km values whereas the smallest diatom Cyclotella meneghiniana exhibited high Ks and Km values for phosphate uptake and assimilation. DCMU inhibited phosphate uptake even at 2.5 µM concentration indicated that the phosphate uptake is mediated mainly by the energy derived from photosynthesis.