A bio-based epoxy 2,5-bis [(2-oxiranylmethoxy)-methyn-furan (BOF) has been synthesized from 2,5-furandimethanol and toughened by its Diels Alder (DA) reaction adduct DA-BOF, which contained a flexible pendant chain. The chemical structures of the synthesized monomers were identified by nuclear magnetic resonance (H-1 NMR and C-13 NMR). The thermal reversibility of DA-BOF was investigated by differential scanning calorimetry and ultraviolet visible (UV vis) spectroscopy. On the basis of the UV vis results, the degree of retro Diels-Alder reaction was determined to be 25-27% in different cured systems. The study of the mechanical properties indicated that when the content of DA-BOF reached 50%, an 85% increase in impact strength could be obtained without seriously sacrificing its tensile strength or modulus. The strategy described in this work could help us to achieve a bio-based epoxy resin with increased impact strength and nearly unaffected tensile properties.