As renewable thermosets, a furan-based epoxy resin, 2,5-bis[(2-oxiranylmethoxy)methyl] furan (BOF), and a furan-based amine curing agent, difurfuryl diamine (DFDA), were synthesized using 5-hydroxymethyl-2-furfural (HMF) and furfurylamine (FFAM), respectively. A novel phosphoruscontaining, furan-based, flame-retardant epoxy (PFFE) was also synthesized using HMF, FFAM and diethylphosphite to improve the flame retardancy of BOF. PFFE had high biomass content and improved the flame retardancy of BOF because PFFE had both furan and phosphorous groups in its molecular structure. To observe the changes in the physical properties following the addition of PFFE, BOF and PFFE mixtures (BOF/PFFE), BOF, and a diglycidyl ether of bisphenol-A (DGEBA) were cured with DFDA, and their thermal, mechanical, and flame retardancy properties were measured and compared. The glass transition temperature, crosslinking density, and tensile strength of the (BOF/PFFE)-DFDA system were enhanced with increased amounts of PFFE. The BOF/PFFE mixture resin (1:1 by wt.) showed comparable tensile strength to DGEBA and had a higher tensile modulus due to the effect of increased crosslinking density and intermolecular hydrogen bonding. Owing to the furan and phosphorus groups, (BOF/PFFE)- DFDA showed remarkably improved flame retardancy by reducing the release of total heat, the rate of heat release, and the spread of fire.