Abstract: In cooling water treatment and in boiler water treatment systems, the hydrolytic polymaleic anhydride, (HPMA)is not a satisfactory corrosion inhibitor. In order to improve its corrosion inhibition, phosphonic acid groups were introduced intramolecularly into the HPMA molecule, and a new compound, PHPMA, is formed. Studied structurally with chromatographic and mass spectroscopic methods together with other analytical determinations, it has been found that both carboxyl groups and phosphonic acid groups are presented in the same molecule, which can be represented by the following structural formula, asThe synthesis of PHPMA can be completed by using HPMA and phosphonic acid, a onestep process. It possesses excellant anticorrosion and antiscale properties, since it has a polycarboxytic acid and a polyphosphonic acid as its own constituents.A good synergistic effect was displayed, it can be used as a anticorrosion agent and a scaling inhibitor in a cooling water system containing chloride ion concentration as high as 40000 ppm.