Results are presented of a detailed x-ray diffraction, Raman and thermal analysis study of the structural phase transitions in LiNH₄SO₄ carried out in the temperature range 298-600 K. Either two or just one phase transition was recorded in the temperature range between 335 and 461 K, depending on the warming process rate. Crystal structures at 298, 318, 383, 423 and 483 K during a slow warming process and at 298 and 523 K during a fast warming process were solved. The transition at 335 K is reported for the first time and consists of a rotation by 41° of the sulphate ion around an S-O bond. The new obtained phase above 335 K is close to the enantiomeric phase at room temperature. The high temperature phase crystallized in the non-polar P2₁nb space group, but the crystal structure obtained removed the spontaneous polarization, according to the calculations made using an ionic model, and agrees with the experimental results.