Tantalum-doped indium tin oxide films were deposited on glass substrate by co-sputtering with two-targets. Tantalum-doping strengthened the orientation of the (400) plane and resulted in better crystalline structure, larger grain size and lower surface roughness. Due to the better crystallizability of the tantalum-doping films, carrier concentration and the mobility were increased. Tantalum-doping revealed better optical–electrical properties. The environmental effects on electrical properties stability and long-term reliability of tantalum-doped films in NaCl, Na2SO4 and HCl solutions at 25°C were also investigated, which simulated corrosion behavior in marine, industrial and acidic environments. The relative resistance change (△R/R) for tantalum-doped films revealed that the films had the best electrical properties stability and long-term reliability in these aggressive environments. The pre-formation of a protective oxide layer on the surface of the films had an enhancing effect on the corrosion properties.