Megalospora occidentalis is a species of corticolous (bark-dwelling), crustose lichen in the family Megalosporaceae.

Found in Australia, it was formally described as a new species in 1994 by lichenologist Gintaras Kantvilas.

The type specimen was collected along the Vasse Highway in Beedelup National Park (Western Australia) at an altitude of 100 m (330 ft); here, in a karri-dominated wet sclerophyll forest, it was found growing on Trymalium floribundum.

The lichen has a thin, pale grey to glaucous-grey thallus that usually has scattered soredia.

The author named it occidentalis because, at the time of writing, it was the only Western Australian species known in genus Megalospora.