For mass spectrometric measurements of δ31S, pure sulphur hexafluoride was prepared quantitatively from different mineral sulphides by the reaction with elemental fluorine under pressure. The results of δ31S measurements on SF6samples were confirmed by comparison of δ31S values with the classical method leading to SO2. Numerous mass spectrometric measurements of SF6and SO2with regard to the experimental conditions of the synthesis, the influence of background, memory effect, and adsorption were made. The measurements of small isotopic variations of sulphur with SF6has advantages in comparison to the SO2technique. The method described can be successfully used for routine work.