The 22-year-old, who is set to star in the wild west-themed comic book adaptation, wore a waist-cinching corset that saw her midriff whittled down to a miniscule six inches wide at its narrowest point.
The actress's usually 22-inch waist was laced into a girdle that reduced its diameter to a miniscule 18 inches.
Megan Fox wore a corset that cinched her waist to a tiny six inches for her role as Leila in the upcoming film adaptation of Jonah Hex
Fox's long skirt was cut away at the front, exposing toned legs clad in red and black stockings and lace-up boots.
'When Megan first slipped into it she almost couldn't breathe,' said a source. 'It's extremely tight - but I think you'll all agree she looks sensational.'
The 22-year-old's character is rumoured to be a prostitute, but studio chiefs are keeping details under wraps
The Tenessee-born model-turned-actress stars in the film alongside Josh Brolin as Jonah Hex.
Details of Fox's role have been kept under wraps, but rumours suggest that her role as Leila is that of a prostitute, possibly explaining the raunchy ensemble.
Electric: Josh Brolin stars as Jonah Hex
'Megan's got an intriguing role in the film,' said the source. 'By day she's the epitome of respectability - by night she's a man-eating vice girl.
'And without giving too much away I can tell you she's one hot ticket in some sizzling scenes.'
Described as a Western with a twist, the film will recount the trials and tribulations of scarred anti-hero Jonah Hex, who tracks a voodoo practitioner attempting to liberate the south with an army of the undead.
The source added that studio chiefs are expecting big things from the film, which will be released next year.
'Josh is absolutely electric as Hex.
'And with Megan providing the eye candy for the lads this film will no doubt be a huge hit.'