A halogen lamp and an acousto-optic tunable filter are used to construct a sinusoidal wavelength-scanning interferometer with the scanning width of 210 nm. A linear wavelength-scanning with the scanning width of 220 nm is utilized to determine amplitudes of three different interference signals produced from multiple-reflection lights by front and rear surfaces of a thin film. Amplitudes of time-varying phases produced by a sinusoidal wavelength-scanning and constant phases in the interference signals are estimated by minimizing a difference between detected signals and theoretical ones. From the estimated values, the positions of the front and rear surface of the thin film with a thickness of about 460 nm are measured with an error less than 4 nm. © 2009 SPIE.