Alexandra Cabot is technically a supporting character in Josie and the Pussycats, but she is such a dynamic character that she almost always overshadows the rest of the cast, in both the comics and the cartoons. She is Alex's twin sister.

Alexandra is a brunette with a white lightning-bolt shaped stripe running through the middle of her hair. In contrast to the good-natured girls in the Pussycats, Alexandra is sneaky, conniving, snobbish, cynical, bitter, and mean. She is insanely jealous of the girls in the band (especially Josie, about whom she never has a kind word). Although Alexandra desperately wants to be the star of the band (and to rename it as "Alexandra's Cool Time Cats"), she is utterly talentless and can't sing or play well at all.

Alexandra has a serious crush on Alan M., and often tries everything she can to try and steal him away from Josie. Although she is not particularly fond of her cowardly snake of a brother, the two of them often join forces in order to try and separate Alan M. and Josie (so that Alex can have Josie, Alexandra can have Alan M., and everyone can live happily ever after...or so they think).

Alexandra also has a black and white pet cat named Sebastian. In the comics, Sebastian is the reincarnation of a witchcraft-practicing ancestor of the Cabot family, Sebastian Cabot. Alexandra finds that, by holding her cat in her arms, she can cast powerful magic spells. (Alexandra and Sebastian's bond is represented in that they both have a matching white stripe in their middle of their hair/fur.) In the cartoons, Alexandra and Sebastian do not have magic powers.

Alexandra's voice in the cartoons is provided by former Mouseketeer Sherri Alberoni , while Don Messick (the voice of Scooby-Doo, Astro, Dr. Benton Quest, Boo-Boo Bear, and more) supplies the meows, screams, and Muttley-esque snickers for Sebastian.

She was played by Missi Pyle in the 2001 live-action motion picture based on the comic book. Sebastian does not appear in the live-action film.