No reason has been given for replacing the long-standing head of the paramilitary group. The US has controversially labelled the group a terrorist organization.
Iran's supreme leader replaced the long-serving chief commander of the elite Revolutionary Guard, state media reported on Sunday.
Brigadier General Hossein Salami will replace Mohammad Ali Jafari, who has served as chief for the past 11 years.
No reason was given for the replacement.
Salami, who is 59 years old, previously served as deputy commander in the Guard. He is seen as a hardliner who is opposed to the reforms of President Hassan Rowhani, such as the 2015 nuclear deal with the West.
Read more: What is Iran's Revolutionary Guard?
In the past, Salami has called for the "annihilation of the Zionist regime" and has threatened the "triangle" of Saudi Arabia, Israel and the United States over a September attack on a military parade that killed 25.
The US controversially reclassified the paramilitary group as a terrorist organization earlier this month.
The group, separate from the military, controls the country's ballistic missile and nuclear programs. It has its own army, air force and naval branches, as well as its own secret service.
aw/rc (AP, Reuters, dpa)