Abstract: A stable orthorhombic superconduting phase LaBa_2Cu_3O_(7-δ), with T_c 82K and Meissner effect 13.6%, has been prepared by citric acid complexation with nitrates. It is determined to be an orderly three layer Ba-La-Ba, oxygen-deficient perovskite structure by X-ray powder diffraction and atomic valence calculation. Through high temperature XRD and DTA-TG study,the phase transition of orthorhombic into tetragonal structure is found to be reversible, and occurs at 450 ℃, not the value 350 ℃ proposed by A. Maeda et al. The superconduting properties are improved as the responsible orthorhombic structure deviates more from tetragonality.