EuNi 2 P 2 was studied with a diamond anvil cell (DAC) and X-ray diffraction (XRD). The structural evolution of powder crystal EuNi 2 P 2 under high pressure up to 137 GPa and its single-crystal structure up to 9 GPa were reported. The unique structural phase transition of this 122-type crystal occurred above 70 GPa in powder crystal EuNi 2 P 2 . The diffraction data from single-crystal EuNi 2 P 2 revealed the coordinate change of the P atom, and the stability of the crystal at 9 GPa was confirmed. The crystal EuNi 2 P 2 remained stable with a tetragonal phase without obvious symmetry changes during compression to 137 GPa.