The reinforcement of polymer matrices with continuous carbon fibers (CF), giving rise to so-called carbon fiber-reinforced polymers/plastics (CFRP) composites is a major issue in the space, aerospace, naval, wind and oil and gas energy industries because of their need for construction materials that exhibit very high structural efficiency (i.e., exceptional strength/ density and stiffness/density ratios). The improvement in interfacial strength between the polymer matrix and reinforcing fiber system leading to the enhancement of overall mechanical performance of CFRPs has always been sought by materials scientists, since the region separating the bulk polymer from the fiber reinforcement is of utmost importance to load transference and distribution. Kim and Mai [1] and Pegoretti et al. [2] discovered that the shear strength of a fibrous polymer composite is closely related to the shear strength of the fibersurrounding polymer matrix domain. They also noted that the latter property strongly depends upon the mechanical performance of the interphase, which constitutes an intermediate, different phase when compared to the reinforcing fiber and the bulk resin [3]. Many efforts were then devoted to build strong fiber/ matrix interphases by controlling physicochemical interactions and frictional forces acting on this particular region of composite systems [4]. That achievement [1, 2] allowed efficient hierarchical composite structures to be technologically addressed and developed, aiming not only to improve the mechanical strength but also to mitigate interlaminar, intralaminar and translaminar damage, hence enhancing the fracture toughness as well [5][6][7]. For instance, the use of fillers such as monolayer graphene [8][9][10] Abstract. In this paper, a cost-effective and eco-friendly method to improve mechanical performance in continuous carbon fiber-reinforced polymer (CFRP) matrix composites is presented. Unsized fiber fabric preforms are coated with self-assembling sugarcane bagasse microfibrillated cellulose, and undergo vacuum-assisted liquid epoxy resin infusion to produce solid laminates after curing at ambient temperature. Quasi-static tensile, flexural and short beam testing at room temperature indicated that the stiffness, ultimate strength and toughness at ultimate load of the brand-new two-level hierarchical composite are substantially higher than in baseline, unsized fiber-reinforced epoxy laminate. Atomic force microscopy for height and phase imaging, along with scanning electron microscopy for the fracture surface survey, revealed a 400 nm-thick fiber/matrix interphase wherein microfibrillated cellulose exerts strengthening and toughening roles in the hybrid laminate. Market expansion of this class of continuous fiber-reinforced-polymer matrix composites exhibiting remarkable mechanical performance/cost ratios is thus conceivable.