Electrocorticography, thanks to its low degree of invasiveness, has received in recent years an increasing attention for chronic brain-machine interface applications. To be up to the task, electrocorticography electrode arrays can benefit from several improvements. Better recording abilities can be obtained through smaller, low impedance and high density electrodes, while conformability can provide superior adhesion to the cortex surface and lower biological impact. In this work we present an ultra-flexible and brain-conformable polyimide-based micro-ECoG array with low-impedance poly(3,4-ethylenedioxythiophene) (PEDOT)-carbon nanotube coated microelectrodes. A first in vivo validation of our device is performed on rat somatosensory cortex.