The 27-year-old actress opens up about the ordeal in the November issue of Vogue magazine.
Asked to name her "deal-breakers" with men, Hathaway replied, "Uh ... fraud?" and laughs.
Raffaello Follieri pleaded guilty to cheating investors out of millions of dollars by falsely claiming he had Vatican connections that enabled him to buy church property at a discount. He was sentenced to 4½ years in prison in 2008.
Jewelry that Follieri gave Hathaway was recently auctioned off by U.S. marshals.
All joking aside, the actress admits the relationship took its toll.
The experience taught her to be "more wary," she said. "It takes a minute for me to let my guard down, but once I do and I get to know someone, I'm very open, very trusting. Some might say too trusting."
Shooting the movie "Love and Other Drugs" opposite Jake Gyllenhaal helped Hathaway move forward, she said. Trust is a theme of the film, and it forced Hathaway to confront the issue.
"I was a wreck from start to finish," Hathaway told Vogue. "I think I cried every single day."
The Oscar-nominated actress is dating actor Adam Shulman.
"Love and Other Drugs" opens Nov. 24.