Yazdegerd II (Persian: یزدگرد دوم), was the fifteenth Sassanid King of Persia. He was the son of Bahram V (421–438) and reigned from 438 to 457.
In the beginning of his reign, Yazdegerd moved his court to Khorasan to face the threat from the Huns. This resulted in Yazdegerd gaining control of Bactria which secured the eastern flank of the Sassanid Empire. In his offensive against the Huns, Yazdegerd's focus shifted to Armenia, Caucasian Albania and the Roman Empire.
Romans had been constructing fortifications in the nearby Persian territory of Carrhae, in anticipation of subsequent expeditions. The Roman Emperor, Theodosius II (408–450), asked for peace and sent his commander, Anatolius, personally to Yazdegerd's camp. In the ensuing negotiations in 441, both empires promised not to build any new fortifications in their border territories. Yazdegerd, gathered his forces in Nishapur in 443 and launched a prolonged campaign against the Kidarites. After numerous battles, he crushed them and drove them out beyond the Oxus river in 450.
During his eastern campaign, Yazdegerd grew suspicious of Christians in the army and the nobility and expelled many of them. He then persecuted the Assyrians Christians and, to a much lesser extent, Jews (he published a decree abolishing the Sabbath, and ordered executions of Jewish leaders, including the Exilarch Mar Nuna). Advancing his pro-Zoroastrian policy, he battled an uprising of Armenian Christians in the Battle of Vartanantz in 451.
In his later years, Yazdegerd became engaged again with the Kidarites until his death in 457. He pursued strict religious policies and persecuted various minorities.