The incorporation of MoO3 affects the structure and properties of iron phosphate glasses. Three series of Mo-Fe-phosphate glasses were prepared with MoO3 replacing Fe2O3 while retaining nominal O/P ratios of 3·1, 3·25 and 3·4. Raman spectroscopy and high pressure liquid chromatography provide information about the molybdate and phosphate anions that constitute glass structures. Decreases in molar volume and increases in glass transition temperature with increasing Mo/(Mo+Fe) ratio are attributed to an increased structural crosslink density through the formation of Mo-O-P bonds between MoO6 octahedra and phosphate anions. The Mo-O-P bonds appear to be more readily hydrolysed in water than Fe-O-P bonds, since the glass dissolution rate increases with increasing Mo/(Mo+Fe) ratio.