Alemanno, agriculture minister under Silvio Berlusconi and mayor of the capital from 2008 to 2013, is suspected of having illegally pocketed €125,000 ($135,240) to finance his political activities.
"I will prove my innocence, although many have already written me off as guilty," Alemanno told journalists at the court.
The hearing was adjourned until Friday so that the court can rule on whether consumer associations can be a party to the case.
On top of the graft allegation, Alemanno has been accused of appointing former militants and friends to city posts.
The case is part of the wider Mafia Capitale scandal in which 46 people are accused of operating a crime group that used extortion, fraud and theft to divert millions of euros destined for public services into their own pockets.
Prosecutors say the network was headed up by Massimo Carminati - a convicted gangster with a history of involvement with violent far-right groups - and his right-hand man Salvatore Buzzi, the go-between with Italy's political world.
Buzzi is the one accused of paying Alemanno €125,000, including €75,000 for electoral meetings, €40,000 for a foundation headed by the former mayor and €10,000 in cash.
In return, Alemanno is alleged to have made sure Buzzi's company won certain tenders and got one of Buzzi's relatives a cushy job. Buzzi was convicted in 1983 of murdering an accomplice in a cheque-stealing scam.
Carminati was given a 10-year prison term in 1998 for membership of a criminal crew which ruled Rome's underworld in the 1970s and 1980s and, prosecutors say, has reinvented itself in the form of Mafia Capitale.