Wearing nothing but a pair of bunny ears on a headband, Cyrus, 26, captioned the snap, "Hoppy Easter."
She added bunny faces to cover her nipples in the photo, which is likely a few years old, as she still had her once-signature short haircut in the photo.
The "Malibu" singer posted a series of other snaps with a more current style to mark the Christian celebration of the resurrection of Christ.
Sporting pale pink shoulder-length waves and a pink seersucker off-shoulder top, Cyrus posed with flowers, sunglasses and other symbols of spring in a series of Instagram videos.
Ratajkowski, meanwhile, posed in black bedazzled bunny ears, white lingerie, pale pink knee-highs and a black corset.
In her photos, the model, one of whose signatures is her long brown hair, rocks a long rose-gold wig and stood in front of a seated Easter Bunny in handcuffs.
"My Easter vibe," she captioned her series of snapshots.
The photos are likely from a recent shoot with Love magazine.
The Inamorata designer posted a video with said Easter Bunny in various sexy-silly poses.