Microalgae are very important organisms as primary producers and have a wide range of applications in areas such as aquaculture, pharmaceuticals, medicine, biofuels, and others. In this study, the effect of temperature and salinity on growth, biomass, proximate composition, and lipid production of Chaetoceros calcitrans (Paulsen) and Thalassiosira weissflogii (Grunow) were investigated. The best growth rate (SGR) and highest biomass production were observed at 30 ℃ and 30 ppt for C. calcitrans and at 30 ℃ and 25 ppt for T. weissflogii. At these optimum temperature and salinity combinations, the maximum cell density was accomplished by day 12 for C. calcitrans (6.74 × 10⁶ cells ml^˗1) and by day 10 for T. weissflogii (3.45 × 106 cells ml^˗1). The proximate composition during this period was 38.25 ± 0.99% protein, 16.96 ± 0.90% lipid, and 9.39 ± 0.59% carbohydrate in C. calcitrans, compared to 13.49 ± 0.28% protein, 10.43% ± 0.25% lipid and 16.49 ± 0.47% carbohydrate in T. weissflogii. Furthermore, over 35% of lipids in C. calcitrans were palmitic acid (C16), while in T. weissflogii, over 24% of lipids were myristic acid (C14). Although C. calcitrans exhibited higher lipid content than T. weissflogii, both species displayed higher levels of saturated (SFA) and monounsaturated (MUFAs) fatty acids and low levels of polyunsaturated fatty acids (PUFAs). The findings illustrated that under their optimum temperature and salinity combinations, both species might produce significant sources of lipids, which can be utilised in various activities such as aquaculture, pharmaceuticals, medicine, biofuels and others.

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