Antimony (Sb) films were prepared by heliconwave-plasma sputtering method. Refractive indices change of Sb films was examined as functions of the film thickness (3.5-100 nm) and sputtering pressure (0.2-0.8 Pa). As the thickness increased from 5 to 15 nm, the phase of the film transformed from amorphous into crystalline and the extinction coefficient X significantly increased from about 3 to 5. Amorphous thin films transformed also into crystalline state by annealing at similar to 200 degreesC and was observed as changes in reflectivity and refractive indices. As the thickness further increased from 15 to 100 nm, the film remained crystalline, however the coefficient k oppositely decreased to the value close to that of the amorphous state (3-4) for films prepared at high sputtering pressure (0.4-0.8 Pa). Furthermore, refractive index n decreased monotonically from about 4 to 2-3 as the film thickness increased and was less dependent on the sputtering pressure,