Commercial cultivation of eukaryotic microalgae has so far employed a unicellular form of species only (e.g., Chlorella pyrenoidosa, Dunaliella salina, and Haematococcus pluvialis). In this study, we assessed the feasibility of using the filamentous eukaryotic microalga Klebsormidium sp. LGX80 as a new cultivar for biomass and lipid production. The effects of different forms and concentrations of nitrogen on growth and lipid production of Klebsormidium sp. LGX80 were studied by using a glass column (o4.5 x 60 cm) photobioreactor under laboratory conditions. Growth and lipid production of the new strain were further evaluated in an outdoor pilot-scale tubular photobioreactor. The results showed that when supplied with urea as a source of nitrogen Klebsormidium sp. LGX80 yielded a final biomass concentration of 8.49 +/- 0.10 g center dot L-1 in which a cellular lipid content was 59.2 +/- 0.4% DW. Under such conditions, the biomass and lipid productivities were 471.7 +/- 5.9 and 248.1 +/- 0.0 mg center dot L-1 center dot d(-1), respectively. Fatty acid analysis revealed that the main fatty acids of Klebsormidium sp. LGX80 were palmitic acid (C16:0), linoleic acid (C18:2 omega 6), and linolenic acid (C18:3 omega 3), of which linoleic acid (C18:2 omega 6) accounted for up to 67.5 +/- 0.1% of total fatty acids. When grown outdoors in a 13,000-L tubular photobioreactor with an initial nitrogen concentration of 3 mM urea, Klebsormidium sp. LGX80 reached the highest biomass concentration of 2.63 +/- 0.09 g center dot L-1 with the cells containing 38.0 +/- 0.5% lipids (% DW), resulting in the volumetric biomass and lipid productivities of 147.2 +/- 3.6 and 37.9 +/- 0.9 mg center dot L-1 d(-1), respectively. The results of light:dark cycle experiment showed that a durative and prolonged light irradiation hindered the biosynthesis of chlorophyll a and chlorophyll b in the cells, but promoted the carotenoid accumulation. These results suggested that Klebsormidium sp. LGX80 can be a potential oleaginous filamentous microalga for commercial production of microalgal oils.