John of Alexandria was a physician and medical commentator active in the 6th and 7th centuries CE. He belonged to the Alexandrian medical school and worked within the tradition of the iatrosophists, professors who produced scholarly commentaries on authoritative medical texts, particularly those of Galen.

His only known work is a fragmentary Commentary on Hippocrates' Epidemics, covering Books 2, 4, 5, 6, and 7. It survives in Greek manuscripts.

John is significant for understanding the transmission of classical medicine in late antiquity. His commentary exemplifies the Alexandrian pedagogical method, which centered on the works of Hippocrates and Galen. This tradition of systematizing Greek medical knowledge was crucial for its later passage into the Arabic and medieval Latin worlds.