Both filamentous microalgae Tribonema and unicellular microalgae Nanochloropsis are promising feedstock for biodiesel production. Nitrogen starvation increased lipid content in Nannochloropsis but decreased that in Tribonema. In this study, biochemical responses of Tribonema under different levels of nitrogen (0N, 0.05N, 0.1N and 1N-BG11) were investigated. 1N-BG11 was sufficient during 15-day-cultivation, while the other levels were nitrogen limited. Cell growth was interrupted with 0N-BG11, but no differences in biomass among 0.05N, 0.1N and 1N-BG11. Both protein and lipid contents (% of dry weight) declined gradually inversely to the increment in carbohydrate contents under the decreasement of nitrogen levels. Both assays and TEM results showed that the cytoplasm in Tribonema contained no starch. Compared to nitrogen-replete condition, the TAG content (% of dry weight) decreased obviously under nitrogen starvation. Different levels of nitrogen did not cause fundamental shifts in fatty acid profiles in Tribonema. (C) 2014 Elsevier Ltd. All rights reserved.