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Gadolinium aluminate perovskite (GdAlO₃) was studied at high pressures of up to 23 GPa in a diamond anvil cell (DAC) using monochromatic synchrotron X-ray powder diffraction. Evidence of a pressure-induced phase transformation from orthorhombic (<i>Pbnm</i>) to rhombohedral (<i>R</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover accent="true"><mrow><mn>3</mn></mrow><mo>¯</mo></mover></mrow></semantics></math></inline-formula><i>c</i>) structure was observed at 21 GPa and further proved by DFT calculations. Before phase transition, the volumetric ratio of polyhedron A and B (i.e., V_A/V_B for ABX₃ general notation) in the <i>Pbnm</i> phase continuously increased towards the ideal value of five at the transition, indicating a pressure-induced decrease in the structural distortion as opposed to the trend in many other orthorhombic perovskites (e.g., CaSnO₃, CaGeO₃, MgSiO₃ and NaMgF₃). Pressure–volume data of the <i>Pbnm</i> phase were fitted to the third-order Birch–Murnaghan equation of state yielding a bulk modulus (<i>K_o</i>) of 216 ± 7 GPa with a pressure derivative of the bulk modulus (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi>K</mi></mrow><mrow><mi>o</mi></mrow><mrow><mo>′</mo></mrow></msubsup></mrow></semantics></math></inline-formula>) of 5.8 GPa (fixed). This work confirms the pressure-induced phase transformation from orthorhombic to a higher symmetry structure previously predicted in GdAlO₃ perovskite.