The authors proposed an iterative imprint method for multilayered nanostructures. A thermoplastic sheet is fed onto a nanostructured mold and thermally imprinted by vacuum pumping between the mold and the sheet. Next, the imprinted sheet is thermally bonded onto a sheet that had been formed in the preprocess and that is held by an upper punch at the position opposite to the mold, and then the upper punch picks the sheet up from the mold. Repeating these processes realizes precision multilayered structures while maintaining horizontal positions of the upper punch and the vacuum-forming mold. This method will lead to the low-cost, high-accuracy fabrication of three-dimensional photonic devices. The authors formed 400x400x270 nm(3) square hollows with an 800 nm pitch on the surface of a polymethyl methacrylate sheet of 1 mu m thickness. The decrease in the light intensity diffracted by the mold surface as a result of the filling of the sheet was monitored in real time during the forming. The authors also successfully bonded another sheet and observed the hollows with 1 mu m intervals in the thickness direction. (C) 2008 American Vacuum Society.