Ab initiostructure determination of new compound (Pb0.6Cu0.4)Sr2PrCu2O7?xwas obtained at 300 and 100 K from X-ray powder diffraction data and refined by Rietveld technique. (Pb0.6Cu0.4)Sr2PrCu2O7?xhas an isotypical structure with TlBa2CaCu2O7(1212) at both 300 and 100 K. At 300 K, crystal data: (Pb0.522Cu0.4)Sr2PrCu206.53, Mr=681.293, tetragonal system, space group P4/lmmm, a= 3.8631(5)?, c= 11.9134(2)?, V= 177.79?3, Z= 1, Dx, = 6.3631 g/cm3, ?=1036.549 cm?1(?=1.54051 ?), F(000) = 299.6, the structure was refined with 31 parameters to Rwp= 4.02%, Rp=2.96% for 3379 step intensities and Rb= 4.80%, Rf=5.17 for 143 reflections, ?goodness of fit? S= 2.20. At 100 K, crystal data: (Pb0.547Cu0.4)Sr2PrCu2O6.89, Mr=692.232, tetragonal system, space group P4/mmm, a= 3.8580(2) ?, c= 11.8898(5) ?, Z=1, Dx= 6.4953 g/cm3, ?= 1053.235 cm?1(?=1.54051 ?), F(000) = 304.6, the structure was refined with 32 parameters to Rwp= 5.53%, Rp=4.22% for 2574 step intensities and Rb= 6.11%, Rf=5.31% for 111 reflection, ?goodness of fit? S= 1.79. Moreover, the composition of Pb was refined to 0.522 at 300 K and to 0.547 at 100 K as compared with the stoichiometric composition 0.6.