This paper presents an extended study on the ion effects of a series of biocompatible hydrated choline based ionic liquids (ILs) on lactate oxidase (LOx), an important enzyme in biosensing technology for the in vitro detection of lactic acid. Secondary structural analysis revealed changes in the protein conformation in hydrated ILs, while thermal unfolding/aggregation dynamics showed different profiles in the presence or absence of ILs. Moreover, LOx thermally denaturised at 90 1C showed residual activity in the presence of chloride and dihydrogen phosphate anions. Kinetic and lifetime studies were also performed, providing a better understanding of the ion effects of ILs on the biocatalytic activity of the enzyme.