This paper reports the development of an advanced thermo-hydro-mechanical (THM) oedometer in order to characterize the behavior of soils under combined non-isothermal and unsaturated conditions. The simultaneous control of temperature, suction and stress states within the sample required rigorous calibration. This THM oedometer accommodates samples 80 mm in diameter and 23 mm in height. The applied vertical stresses can reach values up to 1 MPa, the controlled temperature ranges from 20 °C to 80 °C, and the applied suction is up to 500 kPa. The paper thoroughly discusses the calibration of the device and presents some results of tests performed on a sandy silt.