Rhodium oxide films prepared by sol-gel method exhibit reversible two-color (bright yellow-olive green) electrochromic behavior. The X-ray diffraction analysis and scanning electron microscopy morphology observation suggest that these films are nanocrystalline materials. A significant difference of transmittance for the films at two different color states was observed. The color efficiency at 700 nm was 29.1 cm(2) C-1. The electrochemical behavior of rhodium oxide electrode was measured by using voltammetry method, and the diffusion coefficient of 3.26 X 10(-14) cm(2) s(-1) was determined. The great transmission difference in the visible region at different potential suggests that this film can be used in electrochromic devices.