This study presents a new testing procedure to assess the residual friction characteristics of geo-synthetics-geosynthetics (GSY-GSY) interfaces using an inclined plane (IP) device. The residual friction characteristic corresponds to the friction angle of a GSY-GSY interface determined for a uniform sliding mo-tion condition. A series of tests on a geotextile-geomembrane interface was performed following this residual friction testing procedure. From the results, it was shown that the proposed new testing procedure assessed a residual friction angle φres that did not depend on the “sliding history”. It was shown that this residual friction angle is more conservative than the friction angle obtained from the European standard EN ISO 12957-2 (AFNOR, 2005).