Emicizumab is a prophylaxis for patients with severe haemophilia A with inhibitor. Despite the daily prophylaxis, coagulation states stay below normal value and cannot be assessed by standard hemostasis techniques. In our two patients, we use thrombin generation assay (endogenous thrombin potential (ETP) and Peak) to monitor the patient’s clotting status. Under emicizumab, it is needed to add by-passing agent such as FVIIa (Novoseven®) to avoid bleeding before surgery. By-passing agent dose was chosen with the help of thrombin generation assay and after collegial concertation.