Ignazio Marino arrived for work at Rome's town hall through a side entrance on Friday after stepping down as mayor over an expenses scandal.
"I am very well and am off to a wedding," was his only comment to reporters.
Marino offered to pay back 20,000 euros of expenses opposition parties allege he racked up on private dinners in restaurants using a town hall credit card, but later on Thursday said he would stand down after his Democratic Party withdrew its support.
Marino said his resignation should not be taken as an admission of guilt, but said "political conditions" had made it impossible for him to carry on.
He will continue to run the city until a commissioner is nominated to replace him ahead of municipal elections next year.
Marino was already under pressure amid mounting public anger over the litter-strewn and pot-holed state of the city's ancient streets, a failing public transport system and organised crime's infiltration of the municipal authorities.
The mayor faced calls to resign last year for a series of unpaid parking tickets and saw his popularity slump after a corruption scandal implicated several politicians, including his predecessor, the rightwing politician Gianni Alemanno.
Supporters of Marino, a doctor by profession, say the expenses scandal an other accusations against him were cooked up by enemies whose vested interests he had touched.
He also incurred the wrath of the right by his strong support for gay marriage and the integration of immigrants.
