New polymeric carboxylic acids (11) with widely different solubilities in water were synthesized. The activities of these polymers against the ascitic sarcoma 180 tumor of mice and their acute toxicities in mice were compared with molecular parameters of the polymers such as MW, charge densities and abilities to complex Ca2+ and Mg2+. The maximum effectiveness of these polymers against ascitic sarcoma 180 of mice is greatest for those polymers having fewer carboxyl groups ionized at pH 7. Toxicities are lower for polymers having more carboxyl groups ionized at pH 7.