This article presents and analyses an unpublished account book compiled by Rainier Lascaris (prior of the Benedictine monastery of St. Michael in Ventimiglia and lord of Seborga) in the early 16th century. Preserved in the State Archives of Turin, the manuscript provides essential information on the landed property of St. Michael’s monastery at the end of the Middle Ages and its evolution over the course of time. The presentation of this text is intended to be a first step toward the renewal of studies on the Ventimiglia priory and, in general, on the Benedictine presence in Western Liguria.