BACKGROUND Ethanol may be an attractive carbon source for microorganism growth for the production of several biomolecules. Nonetheless, high amounts of ethanol may be harmful for microbial cells. This study evaluated the effect of adding ethanol to the cultivation of Scenedesmus obliquus, under batch and fed‐batch processes. RESULTS A single addition of ethanol up to 460.00 mg L−1 did not influence cell growth, but above this threshold, different concentrations of ethanol had positive effects on maximum cell concentration. On the other hand, when ethanol was added daily for a period of 10 days, even the smallest ethanol feed rate (5.75 mg L−1 d−1; total added ethanol concentration = 57.5 mg L−1) positively influenced maximum cell concentration. Daily addition of 368 mg L−1 (fed‐batch culture; total added ethanol concentration = 3680 mg L−1) allowed the best cell growth of this study, with maximum cell concentration of 1068.70 mg L−1 and cell productivity of 113 ± 7.13 mg L−1 d−1. Under this condition, the maximum specific growth rate and maximum cell concentration obtained with mixotrophic growth were 2.83 and 2.70 times higher, respectively, than those obtained with autotrophic growth. CONCLUSION Cultures supplied with ethanol significantly improved cell growth. Addition of ethanol by a fed‐batch process allowed the highest biomass production with a total added ethanol concentration that hindered cell growth by batch process. © 2016 Society of Chemical Industry