The effect of applied pressure on α- and γ-NaTiOPO 4 (NaTP) was studied at wide temperature range using the X-ray diffraction technique. Neither a phase transition nor a noticeable cell volume decrease was observed for the α-NaTP polymorph up to 8GPa, even when heating up to 1073K. The applied pressure retains the γ-NaTP structural topology up to 8GPa for r.t. experiments, although a 4% decrease of cell volume had been observed. Hot pressing was found to provoke the γ-NaTP→α-NaTP phase transformation, starting at 773K and 4.45GPa. A complete transition has been observed at 873K and 7.7GPa. A mechanism for the pressure-driven γ-NaTP→α-NaTP phase transition has been proposed.