The Sr1-x Pr x Bi2Ta2O9 (SBT-Pr) ferroelectric ceramic doped with Praseodymium in the range of concentration between 0 and 0.20 was studied. X-ray diffraction patterns show that the Pr-ion substitutes the Sr-ion in the main structure (A21 am space group) and, as a consequence of this substitution the unit cell decreases monotonically. Thermoelectric Analysis (ε vs T) and ferroelectric hysteresis measurements were performed. From the ε-T curves it was observed that the transition temperature depends almost linearly on Pr content. Broad phase transitions were also observed, a typical behavior of ferroelectric materials with diffuse phase transition (DPT). An increase in the diffuseness coefficient is obtained by increasing Pr content according to the Isupov model, due to the higher cationic disorder in the structure, resulting in the loss of the long-range ferroelectric ordering. The hysteresis loop indicates that the substitution of Sr2+ by Pr3+,4+ lowers the polarization due possible to strong pinning domain mechanisms that obstruct long range ferroelectric ordering.