A polarization interferometer capable of measuring film thicknesses ranging from 10 to 3000 is described. A suitable system for measuring thickness of films in resist patterns is designed. The film thickness is measured in terms of the azimuth angle rotation of a plane polarized light. Experimental details are given, along with the results of thickness measurement of Alluminium films. Possible sources of errors and various parameters affecting the precision of measurement are discussed. The measurement error is estimated to be less than 0.1% . The precision of measurement is found to be 30 under normal laboratory conditions and can be improved to 1 by protecting the system from environmental disturbances. With some design modifications, the system could be used for the measurement of very narrow profile of films such as one we meet in the case of the resist pattern. Calculations show that resist films with widths of profile as small as 6 µm can be measured by this method.