Gibbs-energy difference between the gauche and trans isomers of 1,2-dichloroethane (DCE) in liquid and supercritical (SC) CO2 was investigated using Raman spectroscopy. The gauche isomer was relatively stabilized in these solvents compared with in non-polar organic solvents. This was attributed to the interaction of the dipolar gauche isomer with the quadrupole moment of the CO2 molecule, as well as the local density enhancement in SC CO2. Conformation equilibrium of DCE was suggested to be useful as a probe for studying solvent properties of SC fluids.