In a statement on Tuesday, the watchdog said it had received complaints about TripAdvisor from consumers as well as hotel and restaurant owners.
The inverstigation follows consumer complaints received by the Italian watchdog about TripAdvisor.
TripAdvisor, as well as other travel websites, publishes online readers' reviews of hotels and restaurants. These reviews are actually very influental to readers and travellers before they decide to make a hotel booking or visit a restaurant.
However, the authority said that TripAdvisor may have published opinions of people who had not actually been to the places they rated.
In addition, it said TripAdvisor did not make clear enough the distinction between information provided independently by travelers and business profiles that hotels and restaurants pay to get published on the website.
TripAdvisor claims that it takes a tough stance on fraud and that every review goes through a tracking system that uses algorithms to spot patterns of activity.
The watchdog said it would conclude the investigation by August 2015.