We present a new method of imprinting three dimensional (3D) polymeric micro- and nanostructures using, a duo-mold process. In this method, two patterned Si molds are surface treated to have different surface energies. A polymer solution is spin-coated onto one of the molds. forming planarized thin film on the mold. The two molds are pressed together at an appropriate temperature and pressure and then released. The patterned thin film adhering to one of the molds is then pressed onto a substrate at an appropriate temperature and pressure to form supported 3D structures. Alternatively, the patterned thin film on the mold may be released to form freestanding 3D structures. A key success factor in this process is the silane-based surface treatments to enable the patterning of the thin polymer film and final release from the mold to form 3D structures. We demonstrate various polymethyl methacrylate 3D structures with combinations of grating. circular-, and square-patterned molds. The duo-mold process is a potentially low-cost and high-throughput method to fabricate 3D polymeric micro- and nanostructures. (C) 2004 American Vacuum Society.