Lobelia rarifolia is a small herbaceous plant in the family Campanulaceae native to Western Australia.
The erect, slender and annual herb typically grows to a height of . It blooms between September and December producing blue flowers.
The species is found on plains, lateritic ridges and damp flats in the South West, Wheatbelt, Great Southern and Goldfields-Esperance regions of Western Australia where it grows in sandy-clay-loam soils.