Keryo were such holdings as shoryo (individual estates) and shoen (manor in medieval Japan) inherited by kenmon (an influential family) for generations in Medieval Japan.
It was considered that the first example of keryo was of the early shoen which were owned by koshin (the Imperial family) or court nobles who ordered Ie no tsukasa (house stewards) and the like via order documents using a kacho (tag), kafu (code), and iejirushi (house mark showing ownership by the family) to operate the holding from the end of the Nara period to the early Heian period; they were called 'XX keryo' (XX family's holding) or 'XX kaden' (XX family's paddy field).
After the mid Heian period, the Fujiwara clan including the Northern House of the Fujiwara clan, was subdivided into the Kujo line, Ononomiya line, Kanin line and the like, and the Mido line which derived from the Kujo line established the status of Sekke (line of regents and advisers). In that process, shoryo and shoen which belonged to each clan and each house, as well as facilities such as jibutsudo (Buddhist sanctuaries) had assumed functions to control the clan; at that time, the main family such as Uji no Choja (chieftain) or kacho (family head) began to manage them. Those shoryo and shoen were classified according to the kanshoku (official position) and ikai (court rank) of the respective main family, controlled over by the mandokoro (administrative office) of the main family, and the Ie no tsukasa was appointed to carry out the role. Kugen (a standard deed acknowledging a holder's ownership), which was a deed of the keryo, was inherited for generations by an heir such as a legitimate son, along with the kaki (records inherited within the family).
Among the kenmon, the Mido line Sekkan-ke (the families which produced the Regent and the Chief Adviser to the Emperor) owned the biggest karyo. Originally, the shoryo the family owned as the chieftain of the Fujiwara clan mainly accounted for the family's holdings; but later, the kangakuin (a school founded in Heian-kyo [the ancient capital of Japan in current Kyoto]) which was Uji no In (celebrated villa), jiinryo (the holdings of a temple) such as of Hosei-ji Temple or Byodo-in Temple which were temples closely related with the line of the house, became treated as keryo of the Sekkan-ke (the Fujiwara regent's line). Thereafter, as the Sekkan-ke were divided, the aforementioned keryo were transferred as watariryo (land transferred from lord to lord) (also known as denka watariryo), with the rank of sekkan and the chieftain of the Fujiwara clan; the shoryo and shoen which were added to the estate of the Sekkan-ke after the insei (period of rule by a cloistered emperor) was divided among the Konoe family, the Kujo family, and the like; and later, they were established as the keryo inherent to respective five branched Sekkan-ke.