Boron nitride films were deposited by rf reactive sputtering. Optical properties of resultant films were studied as a function of deposition parameters such as nitrogen pressure and substrate bias. Resultant films showed optical characteristics similar to those of hexagonal boron nitride. Composition of the film was determined by X-ray photoelectron spectroscopy. From the IR reflectivity data, transverse optical mode(TO) and longitudinal optical mode(LO) were derived by Kramers-Kronig model. Absorption coefficient was also determined from IR transmission data. Resultant TO and LO frequencies showed that substrate bias caused broadening of reststrahlen band of rf sputtered boron nitride. Refractive index of boron nitride films varied from 1.67 to 3.05 for different deposition conditions. Optical gap of rf sputtered boron nitride films was in the range of 3.8-4.5 eV.