The bulk modulus of nanocrystalline, fluorite-structured samarium doped ceria, Sm0.2Ce0.8O1.9, has been investigated using synchrotron-based high-pressure X-ray diffraction technique. Experiments were carried out under both quasi-hydrostatic condition with silicon oil pressure transmitting medium (PTM) and nonhydrostatic conditions without PTM. The high pressure structural results indicate that the highly defected ionic conductor is stable up to 20 GPa and has a lower bulk modulus than what has been reported for undoped-CeO2. The isothermal bulk modulus of Sm0.2Ce0.8O1.9 is similar to 150-190 GPa compared to similar to 210-220 GPa for CeO2. The collected data experimentally verifies the effect of Sm3+ dopant and oxygen vacancy defect formation on bulk modulus in doped CeO2. The effect of modulus on misfit dislocation formation and dopant ion segregation is discussed in relation to a fundamental understanding of the strain effect in this important family of fast ionic conductors, with potential application as oxygen vacancy conducting solid state electrolytes. (C) 2016 Elsevier B.V. All rights reserved.