In order to improve interfacial properties of adhesively bonded composites, surface modification using Nanoimprint lithography (NIL) is investigated. Since the interfacial propeilies such as bonded strength or fracture toughness are highly depend on a surface morphology, these properties can be improved by designing and fabricating microstntures appropriately in the interface. Considering this fact we introduced NIL technique to the curing process of composites and fabricated microstnictures on the surface of composites, witich gives us stiff interface without any surface preparation such as sand blasting or chemical etching. We simulated the behavior of crack propagation along the interface with Finite element method using cohesive zone model and estimated model apparent fracture toughness of adhesive joints.