In this research, we have investigated the influence of a hydrophobic surface modification of microfibrillated cellulose (MFC) on the mixing properties and uniformity within a poly (lactic acid) (PLA) polymer matrix. On the one hand, the MFC nanoscale dimensions and capacity to form a strongly entangled fibrous network have encouraged the design of new bio-based nanocomposites but on the other hand, its aggregation and flocculation problem has mainly restricted the use of these reinforcements. Especially, the polar nature of PLA was expected to result in enhanced interfacial bonding with MFC fillers, but we observed that the high polarity of MFC compared to the polarity of PLA lead to agglomeration of MFC in the polymer phase. Different MFC dispersions have been produced within a homogenizer by using different interaction chambers of 200 and 87 µm with pressures of 300, 1000 and 1300 bar. Atomic force microscopy (AFM) and rheometry data have been applied to optimize the fiber geometry depending on processing condition. This optimization resulted in the production of high porosity MFC with diameter of 50-100 nm and reduced number of passages. Based on zeta potential data, an evolution of number of hydroxyl groups at the MFC’s surface was observed. Next, MFC has been processed in combination with styrene-maleimide SMI nanoparticles, resulting in the surface modification of MFC by physical absorption of the nanoparticles. The DLS data showed that the SMI nanoparticles are very stable in size under very high shear rate. The interactions of SMI nanoparticles with MFC surfaces (within microfluidizer) were confirmed by AFM. The optimum concentrations for mixing MFC and SMI nanoparticles have been determined by variations in zeta potential and rheometry data, concluding that the best performance depends on a critical concentration of free versus modified hydroxyl groups on the MFC surface. Finally, the modified MFC could be processed on an extrusion line to reach dispersive and distributive mixing in combination with PLA in different concentrations. Keywords: Microfibrillated cellulose (MFC), Styrene maleimide (SMI) nanoparticles.