Effects of modifying the surface of lithium excess layered rock-salt type electrodes by Li3PO4 is investigated using epitaxial Li2RuO3 model electrodes. A 3.6-nm-thick amorphous Li3PO4 layer is deposited on a 25.5-nm-thick Li2RuO3 film by pulsed laser deposition. X-ray absorption near edge structure reveals that the modified Li2RuO3 surface had different electronic states of Ru from the unmodified Li2RuO3 surface, indicating that Li3PO4 deposition changes the structure of the Li2RuO3 surface. Li3PO4-modified Li2RuO3 has a much higher first discharge capacity (296 mAh g−1) between 2.8 and 4.2 V than unmodified Li2RuO3 (190 mAh g−1). The modified and unmodified Li2RuO3 have irreversible capacities in the first charge/discharge process of 22 and 148 mAh g−1, respectively. The surface modification induced by Li3PO4 deposition enhances the structural stability of the Li2RuO3 surface during the initial charging process.