This research is mainly to investigate the thermal and crystalline differences between polyamide 6/montmorillonite (PA6/MMT) and polyamide 6/organo-montmorillonite (PA6/O-MMT) nanofibers, which were both prepared by electrospinning under the same process conditions. The structures of PA6/MMT and PA6/O-MMT nanofibers were observed by scanning electrical microscope. It was identified that the interval between O-MMT clays was increased in the PA6 matrix compared to that of MMT, which was detected by X-ray diffraction (XRD). The thermal properties of PA6 nanofibers contained O-MMT particles were more efficient than PA6/MMT nanofibers, that was verified using thermal gravimetric analysis. The crystalline properties of the electrospun nanofibers was investigated using differential scanning calorimeter and it was found that the degree of crystallinity in the PA6 nanofibers loaded with O-MMT was much higher than PA6/MMT and PA6 nanofibers. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1572-1577, 2010