Abstract: The permeability test with different densities of municipal solid waste (MSW) sampled from a suburban building site of Beijing is introduced. The variation of the seepage coefficient with time during the test is also pre.sented. The test re.suits show that wilh the change of the sample's density the seepage coefficient is able to vary from 10^-3 cm/s to 10^-7 cm/s. It is also noticed that the seepage coefficient reduced with time going, the time for the coefficient to become a constant during the test was about 6 days. So it is supposed that to determine the seepage coefficient of MSW it is necessary to keep the test at least one week.