Novel water-soluble polyphosphazene containing carboxylatophenamino groups (PCPAP) was synthesized by the substitution reaction of ethyl p-amino benzonate with poly(dichlorophosphazene), followed by alkali hydrolysis. Characterizations by IR, H-1-NMR, differential scanning calorimetry, and elemental analysis indicated that the reaction brought about an almost complete introduction of carboxylatophenamino to the polymer side chain. Calcium-crosslinked PCPAP hydrogel beads were accomplished with an extremely mild method. The erosion experiments were conducted in vitro in various pH environments. The erosion duration of the beads at pH 7.4 and 37degreesC was effectively extended by an increase in the concentration of the PCPAP or CaCl2 solution during the preparation process. Moreover, the bead erosion was sensitive to the pH. The sample dissolved 39.4% in a pH 8.0 buffer within 34 days but only 5.36% in a pH 5.0 buffer. Furthermore, PCPAP underwent degradation into macromolecular segments through the breaking of the backbone, and this could prevent accumulation in the body. These properties of PCPAP may be useful for controlled drug delivery, including intestine-specific oral delivery systems.