A new subphthalocyanine (bromoboron trinitro subphthalocyanine) thin film was prepared by vacuum deposition on a single crystal silicon substrate. The ellipsometric spectra of this film have been investigated on an improved rotating analyser polarizer (RAP) type of scanning ellipsometer. The optical and dielectric constants, absorption coefficient and trapping levels of this film in the 400 nm～700 nm wavelength region were given. The spectra were explained and discussed as well.