They are accused of belonging to or having links with a clan allegedly run by the Spada family.
Among those arrested in Ostia, in Rome, was Carmine Spada, known as "Romoletto", who is believed to be the head of the clan.
His brother Roberto - who headbutted a TV journalist, breaking his nose, in November - was also arrested.
The latest mafia blitz - codenamed Operation Eclissi - was carried out by officers from the Italian capital Rome.
Those detained are accused of a range of offences including violence, extortion, intimidation, fraud, drug trafficking, and possessing weapons and explosives.
The city's mayor Virginia Raggi thanked police, prosecutors and the country's interior minister Marco Minniti for the arrests.
She tweeted: "Rome gets a new lease of life with the operation against the Spada clan in Ostia ... Together we say no to criminality. #MafiaGetOutofRome."
The coastal neighbourhood of Ostia is the only one of Rome's 15 districts to be put under direct government control because of alleged mafia infiltration.