The “Victorious Youth” statue, which dates from 300-100BC, was pulled from the sea by Italian fishermen in 1964 off the eastern town of Fano, near Pesaro.
The Italian government, which has been on an international campaign to reclaim looted antiquities, says it was brought into Italy and then exported illegally.
The Getty Museum maintains Italy has no claim to the bronze and says it bought the statue in good faith in 1977 for $4 million (£2.5m).
In announcing its appeal, the Getty Museum said the ruling by the Pesaro court was flawed procedurally and substantively, noting that a previous case involving the statue was thrown out after the judge held, among other things, that the statute of limitations had expired.
“In fact, no Italian court has ever found any person guilty of any criminal activity in connection with the export or sale of the statue,” the museum said in a statement.
The statue, nicknamed the “Getty Bronze,” is a signature piece for the museum.
Though the artist is unknown, some scholars believe it was made by Lysippos, Alexander the Great’s personal sculptor.
In recent years Italy has successfully won back artefacts it says were looted or stolen from the country and sold to museums and private collections worldwide.
Under the 2007 deal, the two sides agreed to postpone further discussion of “Victorious Youth” until the court case was decided.
The Culture Ministry hailed Thursday’s ruling with “great satisfaction” and said it hoped it would lead to serious reflection on the part of the Getty about returning the statue.
The bronze is believed to have sunk with the ship that was carrying it to Italy after the Romans conquered Greece.