Increased world demand for energy and decrease of petroleum reserves have focused worldwide efforts to develop new and renewable energy sources. Liquid microalgal biofuels such as biodiesel represent a sustainable alternative to fossil energy besides being environmentally friendly. However, optimization of culture conditions to maximize productivity (biomass and lipid) is still a great challenge for a commercial biodiesel production. This is due to the difference between optimal culture conditions required for biomass and lipid accumulation. The current study proposes a two-phase method allowing both biomass and lipid increase in Dunaliella tertiolecta. The used this method consists of a first phase when microalgae were cultivated in presence of 2,4-Dichlorophenoxyacetic acid (2,4-D) to enhance algal division and growth. Later, at the end of log-phase, culture conditions were modified by adding NaCl to suddenly increase the salinity from 0.5 M to 2 M. Results showed that combination of auxin with salt stress resulted in a considerable improvement both in growth and lipid production in D. tertiolecta. During the first phase auxin addition improved biomass accumulation by 40% and salt stress in the second phase led to lipid increase from 24% to 70% with the optimal concentrations combination of auxin and NaCl. (C) 2014 Elsevier Ltd. All rights reserved.