Chlorella ellipsoidea were grown in a Mg-free medium. Aliquots of the algal cell were taken out at the beginning and predetermined time intervals during the culture and were analyzed the contents of phosphate in various fractions of the cell constituents. The results obtained were compared with those of the control. When Chlorella cells were grown in a Mg-free medium, the contents of phosphate in the DNA protein, RNA-olyphosphate complex, nucleotidic-lbileP, and PCA-soluble, fractions decreased compared with those of the control, while the content of acid insoluble polyphosphate increased significantly. On the otherhand, RNA-P and lipid-P showed the tendency of decrease at the early stage of the culture, but they were increased more than those in the control as culture proceeds. It is showed that phosphate turnover from acid-insoluble polyphosphate into DNA, protein, and RNA-polyphosphate complex was inhibited by magnesium-deficiency of the cells.