Rathmullen Wood is a national nature reserve of approximately 82 acres (0.33 km2) located in County Donegal, Ireland.

[2] The wood is a high quality example of an old Irish sessile oak woodland.

The large birch trees are a non-native species, and thus do not support the same level of biodiversity as the rest of the woods, and it is actively managed to stop it out-competing the native tree species.

Flora on the reserve include bilberry, bluebells, bugle, hard fern, wild garlic, and woodrush.

Among the birds which inhabit the woods are buzzards, jays, ravens, sparrowhawks, tree-creepers and woodcock.