The immunomodulation of several charged synthetic polymers containing phosphorus in the backbone was studied in vitro through examining their inhibition or promotion effect on the proliferation of both T and B lymphocytes. It is found that polymers based on long chain alkyl ester of tyrosine exhibit immunomodulative activity. Negatively charged polymers show stimulative activiactivity on LPS-induced B lymphocytes proliferation. Positively charged polymers exhibit inhibitory activity on both Con A-induced T lymphocytes and LPS-induced B lymphocytes proliferation.