Phthinosuchus is an extinct genus of therapsids from the Middle Permian of Russia.

Phthinosuchus is the sole member of the family Phthinosuchidae.

Phthinosuchus may have been one of the most primitive therapsids, meaning that its ancestors may have branched off early from the main therapsid line.

[clarification needed] Two species, P. discors and P. horissiaki, have been described.

[1] Phthinosuchus was 1.5 m (5 ft) long with a 20 cm skull, and looked much like the Sphenacodontids, such as Dimetrodon and Sphenacodon.