A　micromechanical　model　of　rough　surface　for　an　interface　between　two　solids　is　presented　to　evaluate　the　acoustic　properties　during　loading　and　unloading　cycle.　By　theoretical　description　of　the　micromechanics　of　rough,　contacting　surfaces　under　static　normal　loads,　the　relationship　between　the　topographic　parameters　of　the　rough　surface　and　the　acoustic　response　of　pressure　interface　are　established.　Ultrasonic　experiments　are　performed　on　three　different　interfaces　formed　by　aluminum　surfaces　with　different　levels　of　roughness.　The　ultrasonic　transmission　coefficient　from　the　interface　is　measured　during　loading　and　unloading　cycles　as　a　function　of　pressure,　from　which　the　ultrasonic　interfacial　contact　stiffness　and　nonlinear　coefficient　are　obtained.　It　is　shown　that　the　nonlinear　coefficient　is　more　sensitive　to　contact　variation　of　interface　under　low　loads.　The　topographic　parameters　of　interface　parameters　are　obtained　by　fitting　measured　transmission　coefficients　using　nonlinear　least　squared　minimization　method.　Using　obtained　parameters,　the　acoustic　properties　of　interface　are　calculated.　The　theoretical　acoustic　properties　are　agreed　well　with　the　experimental　results,　and　it　is　demonstrating　the　capability　of　the　micromechanical　model　of　rough　surface　in　predicting　the　ultrasonic　responses　of　imperfect　interfaces.　©　2011　Journal　of　Mechanical　Engineering.