The 37-year-old reality star and 25-year-old singer were among the celebrities to ring in the holiday in style and post photos of their costumes on social media.
Kardashian wore leather pants and a glittering bra top, belt and choker to channel late singer Aaliyah. Aaliyah, who died at age 22 in 2001, wore a similar look in her music video for "Try Again."
"Baby Girl Aaliyah," Kardashian captioned a photo of her costume Saturday on Twitter.
Lovato, meanwhile, wore a purple jumpsuit as late singer Selena Quintanilla, as seen in a picture Saturday on her Snapchat account.
"I've said it once and I'll say it again, Demi Lovato and Selena Quintanilla are related and y'all can't tell me other wise," one fan tweeted in response to the star's costume.
Reality stars Coco Austin and Joanna Krupa also dressed up for Halloween. Austin and Chanel, her 23-month-old daughter with Ice-T, went as Pink Ladies from Grease, while Krupa channeled the movie's character Sandy.
"Me, my mom, sister and nieces and of course Chanel dressed up as pink ladies," Austin captioned a photo Saturday on Instagram.
Elsewhere, singer Adele posted a first picture of herself in months while in costume. The star, who cut a tour short in July due to damaged vocal cords, wore a glittering dress and elaborate makeup, but didn't explain her look.
"Happy Early Halloween & Happy Birthday Gorgeous," she wrote Sunday.