Nylon-6 and nanoclay/nylon-6 composite nanofibers were prepared by electrospinning technique, in which formic acid was used as a solvent for good solubility of nylon-6. The diameter of nylon-6 and nanoclay/nylon-6 nanofibers was below 350 nm and had smooth surfaces. The DSC heating curves of nylon-6 and composites nanofibers show two endotherm behaviors, Tm1 (about 214 degrees C) and Tm2 (about 220 degrees C), corresponding to the melting events of gamma-form and alpha-form crystals, respectively. The WAXs study showed that the gamma-crystalline phase predominantly present in both nylon-6 and nanoclay/nylon-6 nanofibers. The mechanical properties of the nanoclay/nylon-6 composite nanofibers were higher than neat nylon-6 electrospun nanofibers, which was decreased as the quantity of the clay increased. It might be due to the aggregation of nanoclay at high concentration. The thermal properties of the composite nanofibers were higher than neat nylon-6 nanofibers. POLYM. COMPOS., 2012. (c) 2011 Society of Plastics Engineers