Thin films of Ta2O5 have been deposited by oxygen ion-assisted electron-beam evaporation using 02+ ion energies of 100 eV and 1000 eV. A maximum refractive index of 2.14 and an extinction coefficient of 3 x 10(-4) at 633 nm were found under the optimum conditions of 100 eV ion assistance. The film stress was found to change from tensile to compressive under ion assistance and a maximum stress of -0.4 GPa was recorded. The film hardness also increased with the degree of ion assistance from 7.4 GPa for evaporation only to a maximum hardness of 10.3 GPa for films deposited by ion assistance onto Si. A linear relationship was found between the refractive index and the packing density for films deposited using 100 eV O2+ ions.