Thorius grandis (common name: grand minute salamander) is a species of salamander in the family Plethodontidae. It is endemic to Mexico where it is found in west-central Sierra Madre del Sur in Guerrero. Its natural habitats are pine-fir and pine-oak-fir forests; it tolerates some habitat modification. It usually occurs under logs or the bark of fallen rotting logs. It is threatened by habitat loss caused by logging and expanding agriculture.