The application of modulated UV-visible reflection spectroscopy to the in-situ analysis of passive films is reviewed. After a brief description of the principle and techniques of this method, following recent topics in the analysis of film composition are given: (1) qualitative analysis of passive films on Ni, (2) quantitative analysis of passive films on Fe-Cr and Ni-Cr alloys, (3) in-depth analysis of passive films on a Fe-Cr alloy, and (4) analysis of films on Fe at active-passive transition potentials.