Eustasius of Aosta was a 5th-century Catholic bishop who served as the inaugural leader of the see of Augusta Pretoria, known today as Aosta. While specific details regarding his active ministry are lost to history, he is historically linked to the second Synod of Milan in 451. During this council, he reportedly sent Gratus to represent him, possibly due to his advanced age. His legacy is tied to the early establishment of the Christian community in the Aosta region.