An interference profilometer for measuring the microprofile of superfine surfaces is described. It has a stabilized He-Ne laser light source with two longitudinal modes and two coaxial interference arms. The measuring arm is focused on the sample surface to form a small spot while the reference arm forms a large spot. As a result, the reference arm provides a constant signal and only the measuring arm will be sensitive to the irregularity of the microprofile. Mechanical vibration has a very small effect on the instrument performance. Even if vibration amplitudes reach 300 nm, the measurement noise is less than 1 nm. The instrument has a vertical resolution better than 0.2 Å root mean square (rms) and smallest form error among existing coaxial profilometers. It is well suited for measuring the microstructure on photoetched surfaces. © 2001 Society of Photo-Optical Instrumentation Engineers.