At temperature range of 25–800°C, in situ X-ray diffraction studies on Bi 0.8−x Pr x Ba 0.2 FeO 3 (x≤0.1) ceramics are performed. The unit cell symmetry remains unchanged, while temperature dependence of lattice parameters and unit-cell volumes vary. There are no phase decomposition and structural phase transition detected in the system, which indicate that Pr, Ba co-doping may stabilize the structure of BiFeO 3 ceramic. The unit cell thermal expansion and thermal expansion coefficients are positive. However, for sample with x=0.1, i.e., Bi 0.7 Pr 0.1 Ba 0.2 FeO 3 , the unit cell structural stability decreases, and the thermal expansion coefficient increases. The thermal expansion coefficients abnormal around the Néel temperature are observed, which may suggest a possible antiferromagnetic–paramagnetic transition. It is probably the explanation for their low thermal expansion coefficient during the heating process.