Alemanno, agriculture minister under Silvio Berlusconi and mayor of the capital from 2008 to 2013, is suspected of having illegally pocketed €125,000 to finance his political activities.
The former rightwing politician, whose trial will begin in March, has denied the charges and insisted on Friday the judicial process would "publicly prove my innocence", adding on Twitter: "I have a clear conscience".
Ho la coscienza pulita e non ho nulla da patteggiare. Non ho chiesto riti alternativi proprio per dimostrare pubblicamente la mia innocenza.— Gianni Alemanno (@AlemannoTW) December 18, 2015
On top of the graft allegation, Alemanno has been accused of appointing former militants and friends to city posts.
Alemanno is alleged to have pocketed the €125,000 via his Nuova Italia foundation in return for “acts running counter to his duties in office”, Ansa reported.
The cash was allegedly handed over in October 2014, when Alemanno was no longer mayor and just two months before the first round of 'Mafia Capitale' arrests, according to Italian media reports.
Prosecutors argue that the money was paid by three defendants in trial, which got underway in November.
The three defendants are Massimo Carminati, a convicted gangster with a history of involvement with violent far-right groups, his right-hand man Salvatore Buzzi, who was convicted in 1983 of murdering an accomplice in a cheque-stealing scam and Franco Panzironi, the former chief of Ama, a waste collection firm.
They are on trial with 45 others accused of operating a mafia-style network that used extortion, fraud and theft to divert millions of euros destined for public services into their own pockets.
Alemanno will face his first hearing on March 23rd.
Other politicians, businessmen and officials are also on trial, with all implicated in rigging tenders and other corrupt schemes designed to siphon off cash destined for everything from waste recycling to the reception of newly-arrived refugees.
Much of the trial is expected to be taken up with arguments over whether the accused individuals can be said to have constituted a mafia-type organization as defined by legislation designed to combat more traditional crime syndicates, such as Sicily's Cosa Nostra, the Neapolitan Camorra and Calabria's 'Ndrangheta.
If the prosecution can prove that they did, the defendants will face much tougher sentences than they would if found guilty simply of corruption.