The artwork, named "Where shall we go dancing tonight?", was thrown away by a cleaner who mistook it for a mess from the previous night.
It consisted of cigarette butts, empty champagne bottles and confetti.
The museum has now re-installed the artwork after getting the artists' approval.
The installation at the Museion Bozen-Bolzano was created by two artists from Milan to represent the hedonism and political corruption of the 1980s.
The museum apologised to visitors following the incident, joking it had some "bad luck with the new cleaning lady".
The exhibition will reopen later on Tuesday.
A similar accident happened in Bari, southern Italy, in February 2014 when a cleaner threw away an artwork by Sala Murat.
An art exhibit in Italy has been restored after it was mistakenly binned by a cleaner.