Both　of　the　roughness　height　and　the　roughness　wavelength　are　considered　to　take　effects　in　the　viscoelastic　fluid　lubrication.　According　to　the　correspondence　theory,　the　viscoelastic　fluid　is　seen　as　a　dynamic　system　whose　viscosity　is　described　by　a　transfer　function.　The　shear　rate　is　seen　as　the　input　signal　whose　frequency　is　determined　by　the　roughness　wavelength,　and　whose　amplitude　is　affected　by　the　roughness　height.　After　the　system-response　analysis,　the　relationship　between　the　surface　roughness　parameters　and　the　friction　force　in　the　lubrication　has　been　established.　Under　the　condition　of　the　laminar　flow　and　Reynolds　surface,　the　average　part　of　the　friction　force　is　determined　by　the　thickness　of　the　average　fluid　film,　and　the　amplitude　of　the　periodic　part　decreases　as　the　surface　roughness　wavelength　decreases.　This　theoretical　result　is　proved　by　a　pin-disk　interface　lubrication　experiment,　and　the　viscosity　expressions　in　the　average　Reynolds　equation　is　modified　including　both　the　effects　of　surface　roughness　height　and　the　surface　roughness　wavelength.　Copyright　©　2006　by　ASME.