Abstract The epitaxial growth of the artificial hexagonal GdMnO 3 phase was investigated on substrates with hexagonal symmetries. The GdMnO 3 thin films grown on Pt(1 1 1)/Al 2O 3(0 0 0 1) substrates showed a mixed state of a dominant hexagonal phase and small additional orthorhombic phases, which were stable in bulk. In this study, high oxygen partial pressures during film deposition were found to help to fabricate GdMnO 3 thin films in the dominant hexagonal phase. Also, the growth behavior of the small additional orthorhombic GdMnO 3 phases was studied by X-ray diffraction (XRD) measurements with a synchrotron radiation X-ray source. This study confirmed that even the orthorhombic GdMnO 3 phases prefer specific orientations on the substrates with an in-plane hexagonal symmetry.