Thin films of different dielectric constants were formed depending on the sputtering conditions of a Ta2O5 ceramic sputtered in an oxygen and argon gas mixture using a diode r.f. sputtering apparatus. The dielectric constant was highest at an oxygen percentage of similar to 20% when the sputtering power was kept constant. The higher the sputtering power, the higher the dielectric constant when the oxygen percentage was kept constant. Although the thin films obtained were indicated to be amorphous by electron diffraction analysis, they were crystallized by heating. Electron diffractograms of films with a high dielectric constant indicated alpha-Ta2O5, while those of films with a low dielectric constant indicated beta-Ta2O5.