Interface shear strength between bentonite-polymer composite geosynthetic clay liners (BPC-GCLs) and a textured geomembrane (GM) was investigated and compared to the interface shear strength between conventional Na-bentonite GCLs (NaB-GCLs) and the GM. Lower peak shear strength was observed in BPC-GCL/GM interfaces compared to NaB-GCL/GM interfaces under the same normal stress. Elution of hydrated polymer gel with low shear strength into the BPC-GCL/GM interface was identified as the cause of lower interface shear strength.. Polymer elution was greatest during hydration, but also occurred during shearing.