This paper describes a very simple and rapid method for fabrication of microfluidic devices on the material polydimethylsiloxane (PDMS). The fabrication process is greatly simplified by using a micromachined polymethylmethacrylate (PMMA) master instead of using a silicon photoresist. A PDMS pre-polymer mixture was cast over the PMMA master and cured to produce positive relief structures in PDMS which then served as a mold. This PDMS mold was conveniently used for multiple production of PDMS replicas containing the desired microstructures similar to those on the surface of the original PMMA master. Because our procedure does not require a photoresist, it minimizes the requirement for special equipment and decreases the total fabrication time. Moreover, the method offers the advantage of a wide range of feature size, specifically deeper channels unobtainable with silicon photoresist. Examination of the sidewalls of the channels revealed high fidelity in reproducing the PMMA master via the hardened-PDMS mold. Our protocol enables the production of multiple PDMS-based microfluidic devices in a low-cost and efficient manner.