Jointed interpenetrating polymer networks (jointed-IPN) of epoxy resin and polydimethylsiloxane (PDMS) were synthesized using polydimethyl- siloxane-alpha,omega-diol as the reactive modifier. Since this modifier is fully compatible with the epoxy resins, no phase separation (rubber domain) occurred in the final cured samples. The tree-leaf-type crystals, due to the strain-induced crystallization, were observed in both tensile as well as fracture samples. Although there is no appropriate rubber domain, the experimental results indicate that strain-induced crystallization and the crosslinking density effects of PDMS modified epoxy resins could improve the fracture energy significantly.