(AD359), in early Christianity, one of the several 4th-century church councils concerned with Arianism; (Arianism) it was called by the pro-Arian Roman emperor Constantius II and held at Ariminum (modern Rimini, Italy).

It was attended by some 400 bishops of the Western Roman Empire, with the Eastern bishops simultaneously meeting at Seleucia (now Silifke, Turkey). The majority of bishops at Ariminum were orthodox and accepted the faith of Nicaea, but the Arian minority included skilled diplomats who successfully undid the orthodox decision of the majority when it reached the emperor. The orthodox bishops remaining at Ariminum were then forced to recant and subscribe to an Arian creed drawn up at Nice in Thracia. Pope Liberius soon repudiated this creed and declared the Council of Ariminum without authority.