A special preparation process has been developed to stabilise GdBaSrCu 3 O 7−x compounds in both tetragonal and orthorhombic structures with oxygen deficiency x close to zero. Powder X-ray diffraction analysis (XRD) gives lattice parameters of a = 3.839 Å and c = 11.572 Å for a tetragonal structure, and a = 3.804 Å, b = 3.863 Å and c = 11.588 Å for a typical orthorhombic structure. 155 Gd-Mössbauer spectroscopy reveals via the electric quadrupole i nteraction an asymmetry parameter η = 0.14 (6) for the tetragonal phase (T-phase) and η = 0.31 (5) for the orthorhombic phase (O-phase). The small asymmetry parameter for the T-phase indicates an oxygen disordering in the basal plane. Superconducting transition temperatures T c above 80 K were verified for both tetragonal and orthorhombic phases by resistivity and susceptibility measurements. Despite of a similar T c -value the normal-state transport properties studied by resistivity and Hall effect measurements revealed higher resistivity in the tetragonal phase, which may be caused by both the destruction of the CuO chains and an enhanced scattering introduced by disorder of oxygen atoms in the basal plane.