Tween 80 is a widely used non-ionic surfactant that is added to culture media to make hydrophobic substrate available to microorganisms. Because of this surfactant widespread use, it is important to understand how it affects microbial growth and enzyme production. In this work, the effect of different concentrations (100, 400 and 600 l/L; v/v) of Tween 80 (as the sole carbon source) on the biomass production, esterase activities (assessed through biochemical tests and zymographic assays) and protein content of Fusarium culmorum grown in liquid fermentation was determined. The specific growth rate (μ), biomass yield (YX/S), esterase yield (YE/X), esterase productivity (P), maximal enzymatic activity (Emax), and specific rate of enzyme production (qp) were also estimated. A control medium added with glucose was used. The highest μ was showed in the medium added with 100 l of Tween 80/L. However, the greatest esterase activity was observed in those media containing the highest concentrations of Tween 80 ( energy source and it also induced the esterase production by F. culmorum. Tween 80 concentration is positively correlated with the number of esterase isoforms produced by this fungus. The higher the Tween 80 concentration (400 μl/L and 600 μl/L, v/v), the more number of esterase isoforms will be induced. However, lower concentration (100 μl/L) of Tween 80/L did not show a significant effect on the induction of the esterase activity.400 l/L and 600 l/L; v/v). These results show that Tween 80 was used as the sole carbon and