The genuine notes, held in safe deposit box by UBS in Lugano, are estimated to have been worth €1.5m ($1.84m £1.32m) but should have been exchanged for euros before 2012 – 10 years after the introduction of the euro.
The unnamed beneficiary is taking his case to court to get the money exchanged on the basis that he didn’t know it existed, according to Italian newspaper Il Tempo, which first reported the story.
The 48-year-old bank worker is the sole heir to his wealthy grandfather – a builder from Rome – who also left him property and other cash.
The heir is said to have joined forces with lawyers from the Italian Savers Association which has 50 similar cases where sums of lira have been discovered after the 2012 deadline.
By contrast, in Germany, which has also adopted the euro, the Deutsche Bundesbank has guaranteed that all German mark notes may be changed into euros indefinitely.
Those wishing to exchange marks may do so in person at any branch of the Bundesbank in Germany or by mail.