The fabrication, characterization and application of an 8-channel flexible microelectrode array for recording cortical surface field potentials is described. Polyimide-based microelectrode arrays were fabricated by using photolithography and physical vapour deposition (PVD) methods. Polyimide was chosen as the substrate and insulation material due to its suitable mechanical properties and biocompatibility. Electrodes and transmission lines were formed by sputter-coating of platinum thin films. Microelectrode arrays were characterized and tested successfully in vitro by impedance spectroscopy and in vivo by somatosensory evoked potential (SEP) recordings in rats. These tests indicated good performance and the potential of microelectrode arrays.