An unbranched filamentous green algal strain isolated from Heihe, Zhangye, Gansu Province, China, was deposited at the Freshwater Algae Culture Collection at the Institute of Hydrobiology with accession number FACHB2451. The most outstanding morphological features were relatively long vegetative cells (3-8 times as long as wide), a prominent bilobed chloroplast with median constriction, and both ends terminated in about equally shaped, rounded or tapered. Based on morphological and molecular phylogenetic evidence, the strain was identified as Koliellopsis inundata Lokhorst, which was considered as a new recorded genus and species of freshwater Trebouxiophyceae species from China. The 18S rDNA sequence of our strain showed high similarity with those of type strain K. inundata from periodically flooded agricultural fields in the borderland of Belgium and the Netherlands. The phylogenetic analyses based on 18S rDNA sequence showed that the strains of K. inundata were clustered with other unbranched filamentous Koliellaceae (Koliella, Raphidonema and Raphidonemopsis) into a subclade.