Vivienne Westwood gown covered in shimmering sequins, teamed with bright blue heels and a chic chignon.
Halfway through the show, and the starlet switched into a futuristic PVC-topped Johnny Wujek design to perform new single The One That Got Away, and accept an award for becoming first female artist ever to have five number one singles from one album. (Go Katy!)
Of course the night wouldn't have been complete without just one more frock swap, and Ms Perry changed into a underwear-as-outerwear number by Furne One - consisting of glittering pink corset, high-waist knickers and sheer skirt.
Three looks, one lady, one night. Which is your favourite?
See all the red carpet gowns from this year's American Music Awards below:
Wear pink like Katy at MyDaily Store: