A triaxial testing system developed for testing soils under automatically controlled stress paths and strain paths is described. This system consists of a micro-computer and a pneumatic pressurizing system, together with a mechanically simple system consisting of an ordinary axial displacement-controlled loading frame and an ordinary triaxial cell having a small-diameter piston. Further, since only the cell pressure is adjusted so as to follow the prescribed stress path or strain path at a controlled constant rate of axial deformation of specimen, an accurate peak value together with post-peak behavior can be obtained. Some typical test results of sand obtained by means of this system are presented, which are (1) monotonic drained traixial compression tests of sand at a constant mean principal stress or at a constant axial stress, (2) a cyclic drained triaxial test of sand at a constant mean principal stress involving many intermediate small hysteresis loops of unloading and reloading, and (3) anisotropic compression tests of sand, and (4) cyclic constant-volume tests of sand with taking into account the membrane penetration effects. These results show that this system is a useful and versatile tool for accurately measuring strength and deformation properties of soils loaded under a wide variety of stress paths and strain paths.