The deposition condition to obtain stoichiometric Ta2O5 films, which is still controversial, using magnetron reactive sputtering was studied. The films were deposited by varying O2 gas flow rate with sputtering power and Ar gas flow rate of 200W and 60 sccm fixed. At the conditions of O2 gas flow rate over 20 sccm, amorphous Tantalum oxide films with the refractive index of 2.1 and dielectric constant of 25 were deposited. Among those films, the capacitors dielectric properties of the film deposited at the condition of O2 gas flow rate 50 sccm was best, the leakage current was 1 × 10-8 A/cm2 at the electric field strength of 0.5 MC/cm and the breakdown field strength was over 2.0 MV/cm. This result could be explained from the analysis comparing with a standard sample using RBS because the composition of the film deposited at this condition was closest to the stoichiometric Ta2O5. The result of XPS analysis convinced that this film was stoichiometric Ta2O5 film. A maximum cathode voltage was observed when O2 gas flow rate was 30 sccm. This shows that the Schiller's proposition that one can obtain stoichiometric films at the condition of maximum cathode voltage is not correct and more oxygen than that of the maximum voltage condition is necessary to deposit the stoichiometric Ta2O5 films.