The technique of reactive sputtering has been used for producing tantalum films with various concentrations of interstitial additives like oxygen, carbon, nitrogen, and hydrogen. A number of compounds between tantalum and these nonmetallic elements also have been deposited. The dielectric properties of anodic films on the tantalum formed in an aqueous solution of citric acid have been related to the composition of the tantalum. It was found that the capacitance density of 130v anodic films remains unaffected by the presence of oxygen and hydrogen, while it decreases as the atomic concentration of nitrogen and carbon in the tantalum increases. The dielectric constant, ε, ofanodic films on is approximately 50% of the value of anodic formed on pure tantalum.