Chitosan-coated polyphosphazene-Ca2+ hydrogel beads were fabricated by dropping polyphosphazene into CaCl2/chitosan gelling solution. Polyphosphazene used here was a water-soluble degradable polyanion (PCPAP), which carried almost two carboxylatophenamino groups on each phosphorus atom of the polymer backbone. Two kinds of turbidimetric titration were applied in this study to reveal the interaction between PCPAP and chitosan within the pH range of 4.57approximate to7.14. The effect of gelling solution pH on the properties of chitosan-coated PCPAP beads was especially emphasized. It was found that the PCPAP/chitosan complex prepared at relatively high pH (pH 6.5) dissociated most slowly in pH 7.4 phosphate-buffered solution (PBS). The erosion of chitosan-coated beads and the release of model drug (Coomassie brilliant blue and myoglobin) in PBS were both obviously prolonged with the increase of gelling solution pH, exhibiting perfect accordance with the behavior of complex dissociation. In addition, the coating of PCPAP/chitosan complex on the bead surface facilitated the improvement of drug loading efficiency. The higher the gelling solution pH, the more the drug loading efficiency improved. At pH 6.5 (PCPAP 5%, CaCl2 7%, chitosan 0.3%), the loading efficiency of myoglobin in beads reached as high as 93.2%. These results indicate that the chitosan-coated polyphosphazene-Ca2+ bead is a potential formulation for drug controlled release. (C) 2004 Wiley Periodicals, Inc.