Athanasius I may refer to:
Athanasius of Alexandria (c. 293 – 373), also called Pope Athanasius I of Alexandria, Christian theologian Athanasius I Gammolo (died 631), Syriac Patriarch of Antioch Athanasius I (bishop of Naples) (830–872) Athanasius I of Constantinople (1230–1310), Ecumenical Patriarch of Constantinople