A rationibus was the Roman Empire's secretary of finance, in charge of maintaining the accounts and expenditures of the fiscus which is the imperial treasury. This official's role in the finances of the Early Empire was considerable. The office was originally held by a freedman, but from the 2nd century A.D. and the reign of Hadrian, Equestrians (Equites) assumed total control after the reputation of freedman declined due to corruption. The rationibus was rendered unnecessary by the comes sacrarum largitionum (master of the sacred largess) of the 4th century A.D.

See also , and Aerarium, comes, Congiarium, fiscus, rationalis, and Roman finance.