AbstractReactive forms of oxygen can damage DNA (among other molecules), thus triggering, e.g., atherogenesis and carcinogenesis. However, such dietary antioxidants as lutein and β‐carotene can effectively inactivate them; these compounds were found to high levels in a novel strain (M2‐1) of the microalga Scenedesmus obliquus. The independent and combined effects of pH and temperature on its rates of growth and production of antioxidants were experimentally assessed, via a full factorial experimental design; the effects of each parameter independently, and of their interactions were accordingly quantified by ANOVA. Our results indicated that temperature plays a more important role on the maximum specific growth rate than pH; in terms of antioxidant content, pH and, to a lesser extent, temperature also have relevant effects. Consequently, the highest rate of biomass specific growth (0.294 ± 0.013 day−1) and biomass productivity (0.837 ± 0.054 mg L−1 day−1) were associated with relatively low pH (6) and relatively high temperature (30°C). Conversely, the antioxidant production rate increased with pH; hence, the highest productivity (0.638 mg L−1 day−1) was attained at pH 8 and 30°C. At the best operating conditions for antioxidant content, the levels of lutein and β‐carotene were 203.57 ± 1.41 and 18.20 ± 0.33 mg mL−1, respectively; the maximum production of either one occurred at the early exponential phase. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011