Optical properties, stress and microstructure of Nb2O5 thin films prepared by ion beam sputtering (IBS) are investigated, and the effects of assist ion beam energy and ion current on characteristics of Nb2O5 thin films are systematically discussed. The results show that with different parameters of assisted ion source, the refractive index changes from 2.310 to 2.276 and residual stress varies from -281MPa to -152 MPa. The extinction coefficient of Nb2O5 can be under 10-4, and the surface is very smooth in an optimum deposition condition. Thin films deposited by IBS exhibit better optical properties and microstructures than those deposited by ion assisted deposition (IAD).