Alessandra Mussolini ran in the April 9-10 parliamentary elections with a small right-wing party supporting conservative Premier Silvio Berlusconi. But her party failed to make the threshold necessary to send lawmakers to parliament.
"My bid for Rome mayor certainly is fully confirmed," Mussolini, 43, said in a statement.
At least two other members of Berlusconi's conservative coalition are running in the May 28-29 vote. Mussolini urged the center-right coalition to unite behind one candidate, indicating she might step aside if the center-right agreed on a single candidate.
She said a single candidate was the only hope to defeat Mayor Walter Veltroni of the center-left. Veltroni, a former deputy premier, is considered the front-runner.
Mussolini ran for mayor of Naples a decade ago, losing to a center-left opponent.
Mayoral races are scheduled in several cities, including Rome and Milan, next month. Runoffs, if necessary, will be held June 11.