Blending polypropylene (PP) with high-performance polymers is an efficient way to improve its properties and enlarge its range of applications. Examples of PP and thermostable polymers [1] showed a great improvement of mechanical and thermal properties but presented limitations due to their high processing temperatures. Compared to conventional melt-blending, reactive extrusion consists in synthesizing in situ a dispersed phase during extrusion of the matrix. This one-step, solvent-free process is well-suited for immiscible polymer blends as chemical reactions are occurring at the interface [2]. In our study, polypropylene/polyimide (PI) blends were developed by reactive extrusion, with the in situ synthesis of the polyimide phase in the polyolefin matrix. In the frame of our project, two polyimides were synthesized from commercial diamine and dianhydride monomers. The kinetics of the imidization reaction was studied and confirmed its feasibility in an extruder with a residence time of less than 2 minutes at 200°C. PP/PI blends with a polyimide content varying from 10 to 30 wt% were prepared in a twin-screw extruder in presence of maleic anhydride grafted polypropylene as a compatibilizer. Soxhlet extraction allowed the characterization of the in situ synthesized polyimide phase and confirmed the complete polymerization. Examination of the blend's morphology showed a fine sub-micrometer dispersion of the polyimide phase ranging from 100 to 400nm in diameter. Properties of the blends were deeply investigated to understand the impact of the polyimide phase on the thermal and mechanical properties. [1] Paszkiewicz et al., Characterization of polypropylene/poly(2,6-dimethyl-1,4-phenylene oxide) blends with improved thermal stability. Polymer Bulletin, 2018. [2] Bounor-Legaré et al., In situ synthesis of inorganic and/or organic phases in thermoplastic polymers by reactive extrusion. Reactive extrusion, 2017.