In this work, we evaluate the efficiency of biosurfactants produced by Bacillus subtilis LSFM-05 for the dispersion of acid-treated multi-walled carbon nanotubes (CNT-LQES(1)) and the effect of dispersion on toxicity testing with Daphnia similis. Carbon nanotubes are very hydrophobic materials and they readily agglomerate in mineral water. As a result, in order to determine their toxicity it is critical to evaluate methods to disperse these nanomaterials in a biologically compatible manner. The biosurfactant used in this work, termed BioS, which is a mixture of the lipopeptides (surfactin and fengycin), was found to be non-toxic to D. similis in an acute toxicity test (48 h) and it was an excellent dispersing agent for CNT-LQES(1) in reconstituted mineral water. Monitoring in real-time using the nanoparticle tracking analysis (NTA) showed that the colloidal stability of the CNT-LQES(1) suspension dispersed with BioS was highly stable. These findings are encouraging for the application of biosurfactants as nontoxic dispersion agents in the emerging fields of bionanotechnology and nanotoxicology. (C) 2014 Elsevier Ltd. All rights reserved.