An optical heterodyne profiler has been developed for measuring surface roughness. The height measurement accuracy and lateral resolution are 0. 11 nm and 4 μm, respectively, when a 40× objective is used. A Zeeman-split He-Ne laser is used as the light source. The optical system is designed as a completely common-path interferometer. Optical and electronic common-mode rejection techniques are employed to minimize the effects of environmental conditions. Sample measurements by this heterodyne profiler and other commercial profilers are displayed. The system noise effect is analyzed in detail, the effect of varying the number of samples at each sampling point is shown. The accuracy comparisons of the profiler with different objectives 5×, 10×, 20× and 40× are presented.