A process for preparing a reinforced and reactive thermoplastic composition having a continuous phase based on a thermoplastic polymer and dispersed therein is a discontinuous phase based on a reactive reinforcing agent that may be immiscible with the thermoplastic polymer is provided. A composition obtained by this process is also provided. The reinforcing agent is selected from the group consisting of epoxy resins, polyorganosiloxanes having SiH functional group(s), diisocyanates or polyisocyanates and mixtures thereof, comprises a grafting, a branching and/or a crosslinking, that are carried out in situ, by reactive compounding of these phases with a shear rate greater than 102 s−1, of the reinforcing agent onto the chain of the thermoplastic polymer, so that the discontinuous phase is dispersed homogeneously in the continuous phase in the form of nodules having a number-average size of less than 5 μm.