Ionomers such as Nafion are used combined to redox enzymes in bioelectrocatalysis in order to prevent enzyme leakage and to enhance proton diffusion. In the search for an alternative to this costly and non-ecofriendly material, sulfonated poly(ether ether ketone) SPEEK, another ionomer free of perfluorinated functions can be envisioned. Here, we investigate the effect of ionomer type and concentration on enzymatic oxygen reduction by the Myrothecium verrucaria bilirubin oxidase (Mv BOD). We show that both SPEEK and Nafion ionomers reduce the catalytic activity of Mv BOD in enzymatic assays in solution as well as in electrochemical experiments once the enzyme is co-adsorbed with the ionomer. A pluridisciplinary approach associating microscopy, UV-Vis spectroscopy, dynamic light scattering, SDS gels and electrochemistry allows to point out a molecular interaction between the polymer particles and the enzyme governed by different principles depending SPEEK or Nafion is considered. The differences in hydrophilicity and conformation of SPEEK compared to Nafion account for a more severe effect on enzyme efficiency.