Nanoimprint lithography (NIL) possesses the advantages of sub-10-nm feature and low cost. Nanoimprint lithography patterns the resist with physical deformation using a mold, which can easily reproduce the required nano-scale pattern. However, the variation of environmental conditions and process parameters seriously affect reproduction quality. How to ensure the quality of imprinted pattern is essential for industry. In this study, we used the surface plasmon resonance (SPR) to estimate filling defects, including incomplete mold filling and trapped air bubble. A novel mold structure is fabricated for exciting surface plasmon and a measuring system is set up for defects measurement. Both simulation and experiment demonstrate that the SPR behavior, including the measurable reflectivity change and resonance angle shift, can be affected dramatically by filling defects. Namely, the change of reflective spectrum curve and resonance angle can be used to evaluate the quality of the imprinted pattern. This method sheds light on the problems of detecting imprinting defect and can improve the yield of NIL. (C) 2013 Elsevier B.V. All rights reserved.