The formation of phases in the (R1-xPrx)2Ba4Cu7O 14+δ(Pr-dopedR247;R=Nd, Eu, Tm) system withx=0-1.0 was investigated. Samples of the title series were synthesized at 980-990°C at 25 bar O2, followed by annealing at 300°C under 130 bar O2for 30 hr. Oxygen content of the samples has been determined by iodometric titration. Single-phased samples were obtained withxsmaller than or equal to 0.3, 0.4, and 0.4 forR=Nd, Eu, and Tm, respectively, as indicated by X-ray diffraction measurements. With increasing amount of Pr substituting forR, the cell dimensions of the Pr-dopedR247 phases were found to expand steadily, whereas the corresponding structural orthorhombicity was observed to decrease systematically. Superconducting transition temperatures (Tc's) of the title phases were found to be significantly suppressed upon Pr doping, as indicated by field-cooled temperature-dependent magnetization studies. The effect of Pr substitution onTc's ofR247 (R=Y, Eu, Er, Tm, Nd, Dy) phases was investigated and compared as a function ofR3+radii, but no size dependence effect was observed. In addition, field-dependent magnetization studies for a series of (Eu1-xPrx)2Ba4Cu7O 14+δsamples withx=0, 0.2, and 0.4, respectively, are also reported.