A two-grating interferometer for measurement of profiles of polished surfaces is proposed. The +/- first-order beams diffracted by the first grating produce parallel fringes of about 50-mu m spacing on an object surface. By using the second grating, we eliminate the parallel fringes and extract a phase distribution produced by the surface profile of the object. Moreover, the vibration of the second grating of a small size enables us to use the sinusoidal phase-modulating interferometry. Measurement resolution is higher than 0.3 mu m at the equivalent wavelength of 35 mu m. (c) 2005 Society of Photo-Optical Instrumentation Engineers.