Lichens are the most dominant components in flora of Antarctica. A lichen epiphyte green alga FACHB-2327, isolated from Antarctic lichen Stereocaulon alpinum, was identified as a new species belonging to the genus Deuterostichococcus. The specimen of lichen Stereocaulon alpinum was collected from King George Island, Antarctica. A comprehensive analysis, including morphology, ultrastructure, habitat, phylogeny and secondary structure of SSU rDNA V9 region, was carried out. The green alga FACHB-2327 was described and named as Deuterostichococcus alpinus sp. nov. to recall the continent where it was discovered. The alga FACHB-2327 forms single celled thalli or pseudofilaments up to three cells; cells are cylindrical with mean size 7-18 (20) × 3-5 µm and rounded ends. It can be distinguished from the other species in genus Deuterostichococcus by morphological characters, including cell size, length/width ratio and phylogenetic position using SSU rDNA and ITS rDNA sequences. Keywords: Antarctica; lichen; microalgae; Prasiolales; phylogeny; King George Island.