<p>Bifunctional reactive cyclic carbonate compounds were synthesized and introduced into the epoxy system acting as diluting plasticizer and toughening agent to improve their plasticity and flexibility. Effects of content and structure of cyclic carbonates on the processibility, mechanical performances and thermal properties of the materials were investigated. An impressive improvement in viscosity reduction and mechanical performances is observed by loading of cyclic carbonate. The modified epoxy resin composites exhibit a significant enhancement in mechanical properties at a 30 wt% loading of cyclic carbonate with the tensile strength 170.6% higher than the original resin and 23.9% improvement in the flexural strength. The enhancement in material performance can be attributed to a combination of factors: the presence of soft segments, hydrogen bonding interactions, decrease in crosslinking density, and the plasticizing effect of unreacted components. Moreover, the thermal properties like degradation temperature, T_g temperature and thermo-mechanical properties of epoxy resin composites were also affected by the introduction of cyclic carbonate.</p>