Apollonius of Ephesus was a Christian writer active in the late second and early third centuries CE, during the Roman Empire. He is identified as an ecclesiastical writer from or associated with the city of Ephesus. According to later historians, he was a respected figure who wrote during the reign of Emperor Commodus.

His sole known work was a treatise written against the Montanists, a prophetic movement also known as the Phrygian heresy. This text is now lost, but fragments of it were preserved by the church historian Eusebius. These fragments show that Apollonius criticized Montanist leaders for accepting money and for composing writings that imitated apostolic authority.

Apollonius is a significant figure for understanding early Christian debates. His work represents a major effort by orthodox writers to define correct belief and practice by opposing movements seen as schismatic. Modern scholars view his lost treatise as an important source that provides insight into the specific charges used against the Montanists, concerning prophecy, ethics, and ecclesiastical authority.