A methodology for the rapid fabrication of an injection molding tool, a micromold, for microfluidic components and systems applications is presented. The resulting micromold tooling was utilized to create microfluidic channels in rigid and flexible polymer substrates with depths of approximately 27 µm. While not explored in this paper, the process can theoretically be altered to form channels of varying depths ranging from a few micrometers to approximately 1000 µm. In-plane component dimensions can be varied from approximately 50 µm to cm in width. The tool was made using a photosensitive epoxy (SU-8™) material defined using photolithography on the surface of a rigid substrate. Designs containing complex two-dimensional microchannel/chamber shapes and intersections are achievable using the process. Two polymers were successfully used for injection molding the channels, rigid polycarbonate (Lexan) and flexible polypropylene materials. Plastic replicates of the SU-8™ tool were made with the described process. Fabrication time of the tool was approximately 30 min and it survived 22 shots for polypropylene and 8 shots for polycarbonate without failure. Some deformities of the resulting microchannels were observed and were more pronounced in the PP channels. Channel height was increased by 2-3 µm for both plastic parts due to a ridge that was formed during the release stage of the process. The channel width decreased from the SU-8™ master by approximately 7.9% maximum for polypropylene and 1.9% maximum for polycarbonate.