The influence of lip surface microtopography on lubrication of radial lip seals is studied experimentally and numerically. In the experimental part, lip surface microtopography measured by laser scanning microscope is analyzed using conventional surface profile parameters. Seven surface profile parameters of two seals made of different lip material are estimated and they are compared with the coefficient of friction. It is shown that the seal, which has a larger root mean square (rms) roughness, longer correlation distance and smaller mean peak curvature in the direction of sliding, shows low friction. Based on the experimental results, numerical analysis of hydrodynamic flow at the lip is conducted with a simple sinusoidal wave as a lip surface asperity model. The effects of amplitude, wavelength and peak curvature on the elastohydrodynamic lubrication are investigated respectively. It is demonstrated numerically that seals which had larger rms roughness, longer correlation distance and smaller mean peak curvature shows lower coefficient of friction.