The conduction mechanism in the organic positive temperature coefficient of resistance (PTC) materials composed of conductive carbon black (CB) particles and an insulating polymer matrix was investigated at the nanolevel using a scanning probe microscope. The atomic force microscope (AFM) observation showed the CB particles as circular projections of about 50-100 nm in diameter. On the other hand, nanoscopic current measurements conducted by scanning an An-coated AFM tip an the sample surface revealed that some of these projections also appear as bright spots in the current-mode image, suggesting that these parts are electrically connected through the sample to a conductive substrate. Moreover, the area of the bright regions was observed to increase significantly with increasing applied voltages. These data suggest that the governing mechanism for these organic PTC compounds may be the electron tunneling or hopping processes through the dispersed CB particles rather than the electron transport through the contacted CB particles.