Phosphate controlled release glass (CRG) specimens with varying composition were prepared and their dissolution rates were measured by weight-loss method in leach tests conducted in 30? deionized water. Results show that the release rate of phosphate CRG is highly dependent on its composition. Based on the composition of binary 40Na(2)O-60P(2)O(5) glass, the dissolution rate of phosphate CRGs can be reduced by substitution of divalent metal oxides such as CaO for Na(2)O or trivalent metal oxides such as Al(2)O(3) for P(2)O(5), but increased by introducing B(2)O(3) or SiO(2) into the glass composition. FTIR spectra analysis showed that the composition adjustment caused structural change of the phosphate CRG, which typically demonstrates strengthened M em leader O bond formed by the non-bridging oxygen with the metal ions introduced on the [PO(4)] tetrahedron and the P?O?P bond formed by the bridging oxygen between two [PO(4)] tetrahedrons if its chemical durability is improved.