Background: Contact between blood and the large artificial surfaces within membrane lungs (MLs) is one reason for device-induced thrombus formation during extracorporeal membrane oxygenation (ECMO). Methods: Hemocompatibility testing of gas-exchange fibers (GFs) and heat-exchange fibers (HEs) from commercially available/non-used MLs (ML-type, coating: PLS, Bioline®; Hilite7000LT, X.ELLENCE®; Nautilus, Balance®; EOS, PH.I.S.I.O®) included static hemolysis and platelet adhesion/activation assays. Platelet activation of non-adherent platelets was identified after antibody (CD62P, PAC-1, CD61) and fibrinogen staining (flow cytometry). The surface coverage (%) of adherent platelets was quantified after F-actin filament-staining. Results: All materials were non-hemolytic and did not induce platelet activation. However, platelet adhesion (median (IQR)) depended on the type of surface coating of GFs made entirely of polymethylpentene. Both uncoated GFs (12 (7–19)%) and X.ELLENCE-coated GFs (Hilite-ML, 13 (8–19)%) showed a significantly higher surface coverage compared to Balance-coated GFs (Nautilus-ML, 3 (1–6)%), PH.I.S.I.O-coated GFs (EOS-ML, 2 (2–5)%) and Bioline-coated GFs (PLS-ML, 4 (1–8)%) (p < 0.001). HEs made of polyethyleneterephthalate (Hilite-ML, Nautilus-ML) that were coated with X.ELLENCE were covered with more platelets (5 (3–7)%) compared to Balance-coated HEs (3 (1–6)%), respectively (p = 0.029). Conclusions: In vitro testing disclosed fourfold higher platelet adhesion on X.ELLENCE-coated GFs (and HEs) from the Hilite-ML compared to other ECMO-materials. Additional hemocompatibility tests are necessary to assess the increased platelet adhesion on the materials from the Hilite-ML.