A polymer-based microring refractive index sensor based on slot waveguide was studied at very-near-infrared region (around 890 nm). The relationships between the sensitivity and the waveguide height, width and gap width were analyzed to find optimum design criteria for refractive index sensing. A silicon master mold was fabricated using electron-beam lithography. A unique class of fluorinated polymer, perfluoropolyether, was used to fabricate the flexible soft mold, which was replicated from the silicon mold successfully. The slot waveguide was fabricated on the polymer platform by using UV-based soft nanoimprint technique. The width and the height of the waveguide, and the width of the slot in the slot waveguide, are approximately 510 nm, 830 nm, and 234 nm, respectively. The thickness of the residual layer of polymeric slot waveguide is approximately 350 nm. The fabricated slot walls with a high aspect ratio are shown compatible with low cost mass production processes.