The 30-year-old Hollywood beauty adopted a vegan diet after finishing work on this year's Batman blockbuster "The Dark Knight Rises" and had fake leather shoes specially made for her character Fantine to fit her new lifestyle, reported Daily Star.
But she had no idea director Tom Hooper would be using real, rotten fish to recreate the authentic feel of the desperate streets of 19th Century France as they made "Les Miserables".
"For some reason, for the dock scenes, (Hooper) wanted us to have dead fish, for days, and days and days on end and of course this was the first role that I've done since going vegan, so there I am in period-looking pleather shoes, stepping on dead fish, and I was having a real crisis of conscience, " she said.
Hathaway was not the only castmember struggling to stomach the smell.
"Russell (Crowe) came in... And he just reacted like, 'What is this fetid air?' It's hilarious," she added.