The thermal expansion of the α and β phases of lithium sulphate has been studied using dilatometric and X-ray diffraction techniques. In the α-phase the coefficient of linear thermal expansion is 4.6·10-5 K-1 while in the β-phase the coefficient of linear thermal expansion increases from 0.9·10-5K-1 at room temperature up to 3.4·10-5 K-1 close to the first order phase transition at 575 °C. The volume expansion at the phase transition is 3.2%. In the α-phase the thermal Grüneisen parameter has been calculated to be 0.63 at 705 °C.