In certain application of fiber reinforced polymer composites fracture resistance is required. The aim of this study was to improve the interfacial adhesion between plain woven carbon fiber (CF) and epoxy matrix filled with microfibrillated cellulose (MFC) modified with carboxyl-terminated butadiene acrylonitrile (CTBN) as liquid rubber. CF/Epoxy/MFC/CTBN composite was characterized by different techniques, namely, tensile, bending, fracture toughness (mode I) test, and scanning electron microscope (SEM). The results reveal that at a fiber content 1% of MFC and 10% CTBN, initiation and propagation inter-laminar fracture toughness in mode I improved significantly by 96 and 127%, respectively, which could be attribute to strong adhesion between filled epoxy, CF, and rubber. This can be explained by SEM at given weight as well; SEM images showed that in front of the tip, fiber breakage during initiation delimination as well as the extensive matrix deformation between fibers accounting for increase fracture toughness.