The laboratory hydraulic conducti vita tests with rigid wall permeameter were performed to study the effects of waste leachate on the permeability of a marine clay. The marine clay and waste leachate for this study were sampled from Kimpo Wastefills, and the hydraulic gradients applied to the clay specimens aTe relatively high from 37.5 to 225. The test results show that the permeability of a marine clay is increased with increasing the concentration of leachate and with decreasing the hydraulic gradient. And also both the liquid limit and the plasticity index of the marine clay miRed with waste leachate decrease with increasing the concentration of leachate.