Atomic configuration of a perovskite (ABO(3))-type Na0.5Bi0.45TiO2.925 with oxide-ion conduction is analyzed by a combination of reverse Monte Carlo modelling using total scattering data and the density functional theory calculation, and then local environments around Na, Bi, and the vacancy at the A site are investigated quantitatively. It is found from the obtained atomic configuration that BiO12 has larger distortion compared with NaO12. Moreover, it is demonstrated that a volume around the cation vacancy is larger than those around Na and Bi. On the basis of the results, we discuss effects of the local structures on the electrical conduction properties in Na0.5Bi0.5TiO3-based materials.