[en] Commercial bentonite and a natural clay were used to study the engineering properties of clay-bentonite mixture by compaction test, hydraulic conductivity test and direct shear test. Test results are compared with that of other researchers in an attempt to find the relationship between the properties of bentonite and other natural soils. Explaining briefly the outline about permeameter and testing methods for bentonite in recent years, the authors suggest that hydraulic conductivity test should be conducted simultaneously with break-through test by flexible-wall permeameter on bentonite buffer material for geological disposal of high level radioactive waste. (authors)