Optical properties of bismuth (Bi) film in function of temperature have been investigated by spectroscopic ellipsometry (SE). The solid-liquid phase transition point of Bi thin film is found to be similar to 262 degrees C, lower than that of bulk Bi (271.3 degrees C). The interband transitions of solid Bi occur at 1.82, 3.02 and 4.00 eV, respectively, obtained from imaginary part of dielectric functions and absorption coefficient, which are also consistent with the fitting ellipsometric parameters of the oscillator center energies. A conspicuous difference of optical properties is revealed between solid and liquid Bi, whose characters are semimetal-like and metallike, respectively. The free electron density of liquid Bi is 10(4) times higher than that of solid Bi. The optical properties of liquid Bi film are mainly influenced by free electrons instead of bound ones. However, with the temperature rising, the increase of both direct and indirect band gaps accords with the characteristics of semiconductor, which can be ascribed to the topological properties of Bi film. This work shows the unique advantage of SE on characterizing the optical properties of topological insulators. (C) 2016 Elsevier B.V. All rights reserved.