Demonstrators in many cities braved the cold weather as they descended on main crossroads to renew their allegiance to the country's Islamic principles at a time of rising economic and political pressure.
In the capital Tehran, hundreds of thousands of people and officials descended on the iconic Azadi (freedom) Square, where Iranian President Hassan Rouhani delivered a speech.
A large number of Iranian and foreign reporters covered the event.
Monday marks the climax of the Ten-Day Dawn commemorating the period between February 1, 1979 when Imam Khomeini returned from exile and the anniversary of the Revolution that ended 2,500 years of monarchical rule in Iran.
Every year on this day, the nation turns out in droves to highlight support for the Revolution which replaced the US-backed regime with an Islamic Republic.