The assets comprise properties, money from nearly 30 bank accounts and fine art belonging to Gioacchino Campolo.
Dubbed the King of Videopoker, as he made his fortune by tampering with slot machines, Campolo was sentenced last year to 18 years in prison.
Authorities have described the seizure as the largest ever from a criminal in Italian history.
Campolo came by his fortune by altering slot machines in countless bars and cafes. In 2011, he was found guily of criminal association, usury and extortion.
For 10 years he tampered with gambling machines, amassing millions in illegal profits, the BBC's Alan Johnston in Rome reports.
Among the confiscated assets are more than 200 properties comprising homes, shops and land in Rome, Milan and Paris among other cities.
Campolo also possessed more than 100 art works, including an original Salvador Dali. They are all now state property.
The Italian fraudster is thought to have had strong links with one of the most powerful mafia networks in the southern region of Calabria, known as the 'Ndrangheta.
Authorities say the criminal network helped him amass his fortune in return for sharing some of his profits.
Italian police have hailed the assets seizure as a defining moment in its war against criminal networks.
A police statement said that "taking on criminal fortunes means taking away prestige from the 'Ndrangheta within its own criminal environment".
The 'Ndrangheta is estimated to have an annual turnover of tens of billions of euros, the AFP news agency reports.
But, in 2010, the 'Ndrangheta suffered a major blow when police arrested more than 300 people suspected of belonging to the network following a sophisticated undercover operation.
Italian police have seized assets estimated to be worth about 330m euros (£253m) from a convicted businessman.