Studies on the effect of 10-50 atomic % Ca doping on structural distortions are reported in the present work. Bismuth layered structured ferroelectrics oxides of the composition Sr1-xCaxBi2Nb2O9; with x=0.0 - 0.5 were synthesized by the solid-state reaction method. X-ray diffraction analysis revealed the formation of perovskite ferroelectric ceramic sample and a few additional peaks were observed as concentration of calcium varied from 10 to 50%, gradual shift in peaks with doping is discussed with respect to observed anomalous change in lattice parameters. Also, transformation of structure from pseudo-orthorhombic to pseudo-tetragonal phase is observed at room temperature as concentration of calcium is increased. This suggests that structural distortions are pronounced in such a manner so as to stabilize the structure of unit cell, which may lead to high value of Curie temperature and remanent polarization useful in non-volatile random access memory (NvRAM) devices.