Abstract: We study sound absorption properties of anechoic coatings with different interface shapes. The anechoic coatings with triangle, semicircle, convex rectangle and plate interface shapes were prepared and their underwater sound absorption coefficients measured in a sound tube. The results show that absorption coefficients of the absorbers with single-layer non-planar interface are higher than that with planar interface shapes. In the investigated frequency range, the semicircle interface shape is the best in terms of absorption. It is also found that, at low frequencies, absorption coefficients of absorbers with doublelayer non-planar interface are obviously higher than that with planar interface. The increase of absorption of the anechoic coatings with non-planar interface shapes results from wave conversion of the incident longitudinal wave into shear waves. It is therefore suggested that appropriate design of the interface shapes of the anechoic coatings can enhance underwater sound absorption properties.