As new bio-based epoxy resin systems, glycerol polyglycidyl ether (GPE) and sorbitol polyglycidyl ether (SPE) were cured with tannic acid (TA) at various conditions. When the curing conditions were optimized for the improvement of thermal and mechanical proper-ties, the most balanced properties were obtained for the GPE/TA and SPE/TA cured at 160 degrees C for 2-3 h at the epoxy/hydroxyl ratio of 1/1. The cured SPE/TA had a higher glass transition temperature (T-g) and tensile strength than the cured GPE/TA. Next, biocomposites of GPE/TA and SPE/TA with microfibrillated cellulose (MFC) were prepared by mixing aqueous solution of the epoxy/curing reagent with MFC, and subsequent drying and curing at the optimized condition. For both the GPE/TA/MFC and SPE/TA/MFC biocomposites, T-g and the storage modulus at rubbery plateau region increased with increasing MFC content over the studied range of 3-15 wt %. The tensile strength at 25 degrees C for GPE/TA/MFC biocomposite with MFC content 10 wt % was 76% higher than that of control GPE/TA, while the tensile modulus was little improved. On the other hand, the tensile strength and modulus of SPE/TA/MFC biocomposite with MFC content 10 wt % were 30 and 55% higher than those of control SPE/TA, respectively. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48:425-433, 2010