The method of substitution reaction followed by modification was used to synthesize a novel polyphosphazene containing amino acethydroxamic acid benzyl esters．By changing the feed ratio of reactants during the polymer modification

two resultant polymers with different contents of amino acethydroxamic acid benzyl ester were obtained．IR

1H-NMR and elemental analysis were applied to characterize these polymers．The degradation test in vitro was carried out in phosphorous-free buffer solutions in the pH range of 5.0～8.0．The result revealed that the polymer with certain amount of amino acethydroxamic acid side groups (80％) exhibited strong pH-responsive degradation property．After 1.5 d

the sample dissolved completely in the solution of pH7.4

but lost only about 8％ and 4％ in solutions of pH6.0 and pH5.0

respectively．The degradation rate of polymer accelerated suddenly in the pH range 6.0～7.4．These features are feasible for polymers to act as carriers of oral enteric drug controlled delivery systems．