The activity of the commercial enzyme Candida antarctica lipase B (CaLB), in aqueous solutions of the ionic liquid 1-decyl-3-methylimidazolium chloride, [C10mim]Cl, at pH 7.0 was investigated. The relative enzyme activity (ActIL/ActBf) for ionic liquid molar concentrations ranging from 0.000–0.150 mol L−1 show an increase up to six fold in ActIL/ActBf, with the ionic liquid molar concentration. This phenomenon is shown to be related with the formation of micelles originated by the self-aggregation of [C10mim]Cl. The enzyme activation energy is not affected by the ionic liquid presence, suggesting the absence of structural changes in the enzyme induced by the ionic liquid. It is here demonstrated, for the first time, that it is possible to significantly increase the activity of an enzyme simply by using aqueous solutions of ionic liquids.