Niobium oxide electrochromic thin films were prepared by reactive de magnetron sputtering and their electrochromic properties for Li intercalation and durability were studied. Chronoamperometric analyses revealed that the extended space-charge limited model by Zhang et al. is applicable to Nb2O5 films. Crystallized Nb2O5 films showed excellent electrochromism and stability over many coloration-bleaching cycles. The best performance was obtained for films with a substrate temperature of 500 degrees C and an oxygen flow rate of 10 sccm.