The use of enzymes in laundry and dish detergent products is growing. Such tendency implies dedicated studies to understand surfactant-enzyme interactions. The interactions between surfactants and enzymes and their impact on the catalytic efficiency represent a central problem and were here evaluated using circular dichroism, dynamic light scattering, and enzyme activity determinations. This work focuses on this key issue by evaluating the role of the ethyleneoxide (EO) groups of anionic surfactants on the structure and activity of a commercial lipase, and by focusing on the protein/surfactant interactions at a molecular level. The conformational changes and enzymatic activity of the protein were evaluated in the presence of sodium dodecyl sulfate (SDS also denoted as SLE0S) and of sodium lauryl ether sulfate with two EO units (SLE2S). The results strongly suggest that the presence of EO units in the surfactant polar headgroup determines the stability and the activity of the enzyme. While SDS promotes enzyme denaturation and consequent loss of activity, SLE2S preserves the enzyme structure and activity. The data further highlights that the electrostatic interactions among the protein groups are changed by the presence of the adsorbed anionic surfactants being such absorption mainly driven by hydrophobic interactions. (c) 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1276-1282, 2016