A technique for characterizing thin polymer coatings utilizing an acoustic resonant phenomenon is reported. The acoustic properties (acoustic impedance, sound velocity and density) of a coating on a steel plate were determined by observing and analyzing the echo from the back of the plate. Then, acoustic resonant imaging was demonstrated by scanning with a focused ultrasonic transducer. The thickness distribution of the coating on the back of the steel plate was obtained from the acoustic resonant image and the determined velocity of sound in the coating. (C) 2013 Elsevier B. V. All rights reserved.