The actress looked brilliant as the whacky singer, dressed in a leopard-print catsuit, a bright yellow wig, green eyeshadow, and pink lipstick worked into Nicki's signature pout.
The best bit? The extremely curvaceous rear, which, as we all know, is a million miles away from Miley's own yoga-toned tush.
There's been a lot of competition for the best celeb Halloween costume this year, what with Kourtney Kardashian and Scott Disick dressing up as Batwoman and Robin, Jamie Hince and Kate Moss as Gomez and Morticia Addams, Holly Willoughby as a we're-not-sure-what-but-it's-really-scary, and Gwen Stefani as a dead Sandy from Grease.
Flick through this year's spook-tacular looks and choose your favourite below: