Nowadays, epoxy resins are widely used as structural materials as well as functional materials. They are used in many fields ranging from paint industry to construction and electronics. The versatility of these resins is due to their multiple interesting properties such as their good chemical and thermal resistance. However, they suffer from brittleness which brought about numerous researches to improve their toughness. This work aims to improve the toughness at the interphase between an epoxy resin and a thermoplastic film. The resin used is RTM6 which is qualified for aerospace applications. Among the thermoplastics, phenoxy (PKHH), polyetherimide (PEI) and hydroxyl terminated polyethersulfone (PESOH) are investigated. These pure components as well as PKHH/PEI and PKHH/PEI blends in films form are added to the resin in order to investigate their influence on the latter’s toughness. A preliminary study characterizes morphologically and thermally the thermoplastic blends. Optical microscope observations, DSC and DMTA analyses are performed allowing to observe the blends morphology and to determine their glass transition temperatures. Moreover, the effect of the composition and the process conditions on these characteristics are studied. These analyses show heterogeneous biphasic blends with a sign of partial miscibility. The thermoplastics’ behavior in the resin is then studied. Measures of the interdiffusion of thermoplastics filaments heated in a resin drop show that a heating rate of 2°C/min is the most suitable in order to allow maximized the thermoplastic films diffusion in the resin during curing. Finally, three point bending tests show that all the added films provide an improvement of the resin toughness, the best result being obtained for a PESOH/PKHH 50/50 blend. SEM analyses on failure surfaces indicate that the films bring about a roughness that slows the crack propagation and explains the improvement in toughness.