BSDF (Bidirectional Scattering Distribution Function) has been used in order to predict exact optical characteristic of BLU (Backlight Unit). BSDF implies real scattering characteristics, and measured using test equipment of Goniometer type and compared simulation results with measuring data. Simulation was performed for direct-type LED BLU and CCFL BLU by applying BSDF for diffuser sheet, diffuser plate, and reflector. Accuracy of total flux and luminance, viewing angle, image, etc. was increased and simulation result was obtained in a short time using BSDF assuming multiple sheets as one sheet.