Inorganic solid-state electrochromic devices (ECDs) based on tantalum oxide (Ta2O5) as ion conductor layer were fabricated by vacuum cathodic arc plasma (CAP) deposition. This work focuses on key factor of fabricating Ta2O5 film deposited by CAP through four different ratios of oxygen and argon. Our results show that refractive index mostly decreased with increasing oxygen flow rate. Refractive index of 1.9 was achieved for Ta2O5 film with O-2/Ar = 2.4 which provided high ion conduction pathways through a highly porous structure. We also observed higher ionic conductivity sigma(1) = 3.5 x 10(-6) S cm(-1) for Ta2O5 film at O-2/Ar = 2.4 which enhanced ion's mobility for ECDs causing rapid coloring/bleaching phenomenon. As a result, excellent optical density and rapid response times were observed in fabricated device with an area of 20 cm(2), exhibiting optical density of 0.63 (@ 550 nm) and transmittance variation T = 50% (@550 nm) with the bleaching time = 5 s and transmittance variation T = 50% (@550 nm) with the coloring time = 13 s.