This study aimed at evaluating the influence of magnetic field on the growth and biomass composition of Spirulina sp., cultivated in vertical tubular photobioreactors. Magnetic fields of 5, 30 and 60 mT generated by electric current and ferrite magnets were applied at different lengths of time. The magnetic field of 30 and 60 mT for 1 h d(-1) stimulated the growth, thus leading to higher biomass concentration by comparison with the control culture. Increase in productivity, protein and carbohydrate contents were 105.1% (60 mT for 1 h d(-1)), 16.6% (60 mT for 24 h d(-1)) and 133.2% (30 mT for 24 h d(-1)), respectively. These values were higher than the ones of the control. Results showed that magnetic field may influence the growth of Spirulina sp., since it triggers a stimulating effect and can leads to twofold biomass concentration in equal cultivation time periods. (C) 2016 Elsevier Ltd. All rights reserved.