Manganese(IV) oxide is the inorganic compound with the formula MnO2. This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules.

Manganese dioxide was one of the earliest natural substances used by human ancestors. It was used as a pigment at least from the middle paleolithic. It was possibly used first for body painting, and later for cave painting. Some of the most famous early cave paintings in Europe were executed by means of manganese dioxide.