None of the original seven candidates won an absolute majority in the first round last week, necessitating a runoff between the two top candidates.
The Iranian News Agency said Iran's spiritual guide Ayatollah Ali Khamenei and President Mohammed Khatami cast their votes Friday in the second round.
Both Khamenei and Khatami urged eligible voters to turn out en masse at the polling stations and cast their votes to exercise their democratic right.
"The Iranian people will be the main winner of the elections, because the higher the turnout, the better it is in the sense of protecting the country and safeguarding the people's pride," Khamenei was quoted as saying.
For his part, Khatami stressed that a high turnout "will be for the sake of freedom and democracy and will help confront dangers and challenges."