The　optical　properties　of　hexagonal　boron　nitride　(h-BN)　thin　films　were　studied　in　this　paper.　The　films　were　characterized　by　Fourier　transform　infrared　spectroscopy,　UV-visible　transmittance　and　reflection　spectra.　h-BN　thin　films　with　a　wide　optical　band　gap　E-g　(5.86　eV　for　the　as-deposited　film　and　5.97　eV　for　the　annealed　film)　approaching　h-BN　single　crystal　were　successfully　prepared　by　radio　frequency　(RF)　bias　magnetron　sputtering　and　post-deposition　annealing　at　970　K.　The　optical　absorption　behaviour　of　h-BN　films　accords　with　the　typical　optical　absorption　characteristics　of　amorphous　materials　when　fitting　is　made　by　the　Urbach　tail　model.　The　annealed　film　shows　satisfactory　structure　stability.　However,　high　temperature　still　has　a　significant　effect　on　the　optical　absorption　properties,　refractive　index　n,　and　optical　conductivity　7　of　h-BN　thin　films.　The　blue-shift　of　the　optical　absorption　edge　and　the　increase　of　Eg　probably　result　from　stress　relaxation　in　the　film　under　high　temperatures.　In　addition,　it　is　found　that　the　refractive　index　clearly　exhibits　different　trends　in　the　visible　and　ultraviolet　regions.　Previous　calculational　results　of　optical　conductivity　of　h-BN　films　are　confirmed　in　our　experimental　results.