Imam Khomeini, the founder of the Islamic Republic, passed away on June 3, 1989 at the age of 87.
A large number of people are expected to converge at the mausoleum of Imam Khomeini in southern Tehran to pay their tributes.
Several officials, scholars and researchers as well as ambassadors and diplomats residing in Iran will take part in the ceremony.
Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei will address the gathering of mourners at the shrine.
Similar mourning processions will also be held throughout Iran and in some other countries.
Processions and gatherings are held each year to pay homage to the late founder of the Islamic Revolution and to renew allegiance to the ideals of the Islamic Revolution.
Grand Ayatollah Seyyed Rouhollah Mousavi Khomeini, better known as Imam Khomeini, was born to a family of religious scholars in 1902 in the central Iranian city of Khomein.
Imam Khomeini contributed many years of his life to standing up to the US-backed Pahlavi dynasty. He had eventually paved the way for its downfall in the 1979 Islamic Revolution.
Imam challenged colonial powers and confronted their dominance by restoring awareness among the oppressed nations.
Imam Khomeini, who passed away on June 03 1989, is considered a high-caliber religious scholar, is followed by followers of various divine religions and freedom seekers.
Imam revived divine values at a sensitive juncture of history when the world had been plunged into social and moral decline.