We have performed density-functional theory calculations for Li4Ti5O12/Li7Ti5O12 (LTO/Li-LTO) interfaces and made a detailed analysis of the local atomic and electronic structures. In the bulk regions of the supercell, the atomic and electronic structures are well reproduced to be similar to those of the LTO and Li-LTO bulk crystals. The present (001) interface models show abrupt structural changes between the cubic spinel-based LTO and ordered rock-salt Li-LTO phases, while there occur no substantial strains around the interface due to the little volume change or lattice mismatch. Thus, the calculated interfacial energy is very small. The calculated O-K electron energy-loss near-edge structure/X-ray adsorption near-edge structure (ELNES/XANES) spectra in the bulk regions are similar to those of the bulk crystals, while the O-K edge spectra at the two kinds of interfaces have specific shapes, differently from the simple superposition of the bulk spectra. The preferential occurrence of the (001) interface can be understood from the preferential Li diffusion along the [110] direction in LTO and the small interfacial energy.