Sakellarios (Greek: σακελλάριος) is an official entrusted with administrative and financial duties (cf. sakellē or sakellion, "purse, treasury"). The title was used in the Byzantine Empire with varying functions, and remains in use in the Eastern Orthodox Church.

In the Byzantine times the sakellion of the emperor also kept records of imperial monasteries and their property. Therefore the sakellarios was also an administrative title, which was given from the 7th century to the general comptroller of the state finances, i.e. the finance minister of the Byzantine Empire. Etymologically the word derives from the Latin sacellus, a purse for coins. Note that the Modern Greek word sakoula, bag, has the same origin. The Byzantine Empire was the legal heir of the Roman Empire and its founder, Constantine the Great, was a Roman. Thus, the official in charge of the emperor’s pouch, i.e., the treasury, was the sacellarius.

As monasteries also have treasuries, the title is also found in the Greek Orthodox Church hierarchy. In later years the title was replaced by that of the Grand Treasurer (Megas Thysaurophylax); however it remained unaltered in the Ecumenical Patriarchate of Constantinople’s structure. In the Synod of Ferrara-Florence (1438-9), that was supposed to unify the Greek Orthodox and the Catholic churches, the Ecumenical Patriarch had included in his entourage the Megas Sakellarios (among other officials and bishops).