Gessius of Petra (Greek: Γέσιος, Gesios) was an Arab physician, iatrosophist and pagan philosopher active in Alexandria in the late 5th and early 6th century.
Gessius was a native of the region of Petra. According to Damascius, who is the main source for Gessius' biography in the Suda, he was from Petra itself. Stephanus of Byzantium, on the other hand, writes that he came from the agricultural region of el-Ji (today Wadi Musa) not far from Petra. His father's name is unknown. He may have been descended from the Gessius who was a student and correspondent of Libanius and was active in Egypt in the 4th century. He studied under Domnus, who was Jewish. Later, he is said to have lured students away from his master.