Ta2O5 films were deposited at room temperature by radio frequency(RF) sputtering with the target of bulk Ta2O5, in Ar or Ar-O2 mixture atmosphere. The reflectivity spectra measured from two sides of a film are compared to evaluate the optical absorption of the film. It is found that the excess optical absorption arises from deficiency in oxygen during sputtering. These defects can be eliminated effectively by selecting adequate Ar-O2 mixture and power for sputtering, and unabsorbing Ta2O5 films with compactness and smoothness can be obtained without annealing.