Abstract: A new triaxial testing system which could control suction in wetting-induced collapsible tests was successfully developed to study suction effects on wetting-induced collapsible deformation.The pedestal of the triaxial cell was made up of two major parts,and the equipment not only could control suction but also could make water accessible to soil.A pressure / volume controlled equipment was combined with the triaxial system to measure the water volume absorbed by samples accurately and to add pressure on water to filtrate into the samples.The apparatus could measure volume change precisely and keep deviator stress unvaried as well as measure the volume of water filtrating into the samples exactly.A triaxial collapsible testing procedure was described using the new apparatus for undistrubed collapsible loess with controlled suction.Furthermore,a series of double triaxial collapsible tests were conducted under different suctions and the same net cell pressure,and tests under different net cell pressures and the same suction were also done.It was indicated that the collapsible deformation increased with the increasing suction,and the effect of the net cell pressure on collapsible deformation was remarkable.The new triaxial system was a useful facility to study wetting-induced collapsible behavior of loess.