In the present work, we investigated the thermo-viscoelasticity and fracture toughness of various cured blends of two epoxy monomers with different molecular weights: 380 (Epikote 828) and 900 (Epikote 1001). The blended resins were easily prepared, and miscibility (no phase separation) in the blended resins was expected. The composition of the blended epoxy resins ranged from 0 to 100% by weight of the Epikote 1001. The measured damping factor and dynamic loss modulus in the glass-transition confirmed that each blended resin had a single phase, i.e., they were miscible. The fracture toughness at room temperature increased modestly with the Epikote 1001 content over the whole range (0-100 wt%). We found that below the glass-transition temperature, the macromolecular modifications enabled tailoring of the fracture toughness while maintaining the glassy bending modulus and with little change in the glass-transition temperature.