A new method called "Darcy tracer test" was successfully employed to determine both the hydraulic conductivity and effective porosity of different swelled clays with various total porosity or density. The nearest results showed that it is possible for clay to have high total porosity but very low effective porosity and low hydraulic conductivity. It is due to the occurrence of dead pore when clay is swelled. Besides, the latest results of this project successfully developed a process to determine the dead pore porosity, effective porosity and porosity of double-layer absorbed water of swelled clays.