After the deliberate investigation into the newly unearthed epitaph of Li Shengcai (a Buddhist nun, the younger sister of Li Rangyi who was a prime minister in the later Tang Dynasty) at Qujiang village in Xi'an, and with the mutual proof of historical documents, the genealogy, the official titles, prefecture locations related to Prime Minister Li Rangyi are discovered. Li Rangyi neither belonged to the family Li at Longxi (隴西), nor to the family Li at Zhao jun (趙郡). He died virtually on the way from Yang zhou (揚州) to Chang'an (長安), not on his duty as high military officer in Dongchuan (東川). Eventually, this discovery offers new materials for the the research on the Late Tang society.