Ammia of Philadelphia (fl. late 1st–early 2nd century AD), also known as Ammia the Prophetess, was an early Christian prophetess in the Christian community of Philadelphia, located in the Roman province of Asia (Alaşehir, Turkey).

She was one of the few women in the early church formally recognized as a prophetess, noted for her contributions to the prophetic tradition and her role in shaping early Christianity. Acknowledged by the historian Eusebius, she is regarded as a successor to the apostolic prophetic ministry, adhering to orthodox traditions and contributing to the foundation of the early Christian churches of Asia.

Ammia was a prophetess who was well-recognized in antiquity and referred to as "Ammia in Philadelphia" by Church historian Eusebius (4th century CE) in Ecclesiastical History, (Chapter XVII.—Miltiades and His Works). Catholic Answers mentions that "[she] must have belonged to the primitive Church of Philadelphia," linking her association with the early Christian community there. Eusebius listed her as part of a distinguished group of prophets, among Agabus, Judas Barsabbas, Silas, the daughters of Philip, and Quadratus, many of whom are referenced in the Book of Acts. Ammia was regarded as a successor to the prophetic tradition established by figures like Philip's daughters, New Testament prophetesses active in the 60s CE. While Philip's daughters were prominent in their time, Ammia later "succeeded them in fame," gaining reverence throughout Asia Minor.

Ammia was active in the church from the late 1st to early 2nd century CE, contributing significantly to the prophetic tradition during Christianity's formative years in Asia Minor. She flourished between approximately 100 and 160 CE, with her influence as a prophetess widely recognized in the first half of the 2nd century. Scholars such as Christine Trevett and W.M. Ramsay align her ministry with the period following Quadratus, who was active in the 120s CE, and suggest she may have been succeeded by the Montanist prophets in the 160s. Dr. Catherine Kroeger notes that the first preserved mention of Ammia dates to around 160 CE.

Ammia was acknowledged within the orthodox Christian tradition, which emphasized adherence to mainstream Christian beliefs. Additionally, this view was supported by Eusebius, whom he identifies her as one who "prophesied under the New Convent". This recognition sets her apart from contemporaries like Priscilla and Maximilla, who were associated with Montanism, a movement later deemed heretical. Despite this distinction, the Montanists attempted to claim Ammia and Quadratus as predecessors in the prophetic gift. They sought to connect their movement to the established tradition of prophecy within the early church.

Ammia's prophetic practice was noted for its measured and composed approach. This contrasted sharply with the ecstatic and frenzied style of Montanist prophets, which Eusebius criticized as deviating from established traditions.

Eusebius references Ammia as part of a lineage of distinguished prophets in early Christianity.

Eusebius quotes Miltiades, a contemporary critic of Montanus, who writes: