Self-healing capacities of geosynthetic clay liners (GCLs) have been investigated using laboratory leakage rate tests. Two types of GCL were tested. The first type was a geomembrane supported GCL (GM-GCL) and the second type was geotextile encased GCL (GT-GCL). The diameters of the defects investigated ranged from 5 to 50 mm. Overburden stress (sigma) varied over the range 0-200 kPa. Tap water, a solution of 10 g/l of NaCl in tap water and a solution of 100 ml/l ethanol in tap water were used as the liquid permeants. The test results indicate that for both GM-GCL and GT-GCL, defects with diameters less than 30 mm can be self-healed providing the liquid is tap water or the ethanol and tap water solution. Factors that tend to reduce the thickness of the diffusive double layer around particles of bentonite tend to reduce the self-healing capacity of a GCL, and the free swelling index of bentonite used in a GCL can be used to evaluate the self-healing capacity. The applied stress has two possible effects on self-healing capacity. One is the squeezing of hydrated bentonite into the damage hole and another is limiting the amount of hydration-induced expansion of the bentonite. For the conditions tested, the self-healing capacity increased with increasing applied stress. (C) 2013 Elsevier Ltd. All rights reserved.