Dark Saber (also known as "Saber Alter"), is a villainess from the Fate series. She is the dark, evil version of the proud, idealistic servant Saber. She is voiced by the same seiyuu that voices Saber herself, Kawasumi Ayako.

Saber Alter makes several appearances in both the Fate series and Carnival Phantasm; in the Heaven's Feel route, Saber becomes corrupted by the darkness by Angra Mainyu and becomes Dark Sakura's servant, Saber Alter. Saber Alter abandons the ideals that the original Saber had, which easily disgusts Gilgamesh as he prefers the more idealistic Saber when she was resisting him.

In Carnival Phantasm, she has several cameos in Episode 7 as both a figure and a figma, and in Episode 8, Saber becomes so angry and frustrated with Gilgamesh that she transforms into Saber Alter, whose darkness instantly attracts the men eating at Ahnenerbe, including Gilgamesh. She later reverts back to her old self as standard Saber when she comes back home to Shirou from work.