Abstract The stability of phases in the (Y 1-xPr x) 2Ba 4Cu 7O 15-δ (Pr-doped 247) system with x= 0 to 1.0 was investigated. The samples in the Pr-doped 247 series were prepared at 990°C under 20–24 bar of oxygen atmosphere, followed by long time annealing at 300°C under 120 bar of oxygen pressure. Nearly single-phase samples were obtained only for x≤0.6–0.7 based on X-ray diffraction data. The lattice parameters of the Pr-doped 247 samples increased monotonically with increasing x due to the larger size of Pr. The superconducting transition temperature (T c) of Pr-doped 247 samples determined from resistive measurements and field-cooled magnetization was found to be in good agreement and decreased from 88 (x= 0) to 21K (x= 0.6) with increasing x.