Glasses in the systems xFe₂O₃-(45-x)K₂O-55P₂O₅ and yFeCl₃-10Fe₂O₃-(35-y)K₂O-55P₂O₅ have been prepared over a wide range of composition (x = 0-11.5 mol% and y = 0-30 mol%). The thermal expansion coefficient, glass transition temperature, density and dissolution rate in HCl (1.6 M) at 60 °C were investigated. Results indicate that increasing Fe₂O₃ content in potassium phosphate glasses increases the density and glass transition temperature, while the thermal expansion coefficient and dissolution rate decrease. The same behaviours were obtained when FeCl₃ content was increased. These results indicate that the chemical durability of potassium phosphate glasses would be enhanced upon addition of Fe₂O₃ and/or FeCl₃. The infra-red spectral analyses of the glasses reveal a significant structural change in the glass matrix depending on the composition. The incorporation of iron (as iron oxide or iron chloride) into the potassium phosphate matrix depolymerizes the glass structure through formation of P-O-Fe(III), P-O-Fe(II) and P-Cl bonds. The depolymerization process was found to be more sensitive for glasses with x+y<25 mol%.