A new optical method for angle measurement based on totalinternal- reflection heterodyne interferometry is presented. In this method, heterodyne interferometry is applied to measure the phase difference between s and p polarization states at total internal reflection. This phase difference depends on the angle of incidence. Hence, smallangle measurement can be performed only by evaluating this phase difference. The validity of the method is demonstrated, and it has a measurement range of 10 deg. Its resolution depends on the angle of incidence; the best resolution is 8×10-5 deg.