In this study, the marine alga Tetraselmis suecica was cultured in F/2 medium with various rang of salinity and pH. The influence of stressed algal cells to produce biofuels was studied. The neutral lipid (triacylglycerol) assembled by T. suecica was determined using Nile Red dye under salinity stress (up to 1 M NaCl) and pH (pH 7 to 9). Salinity showed a stimulating effect on triacylglycerol in the algal cells at the 1 Molars, while the effect of pH was changeable. Then fatty acid profile of T. suecica cells was evaluated by gas chromatography-mass spectrometry (GC-MS) after direct trans-esterification with hydrochloric acid in methanol. It was shown that, high salinity was ideal for biodiesel production due to increasing of monounsaturated fatty acids produced by Tetraselmis suecica.