In this study, clay-dispersed polystyrene (PS) nanocomposites were prepared with the in situ atom transfer radical polymerization method and were subsequently electrospun to form nanofibers 450-650 nm in diameter. The polymer chains extracted from the clay-dispersed nanofibers exhibited a narrow range of molecular weight distribution. Thermogravimetric analysis (TGA) confirmed a higher thermal stability of the resulting nanocomposites compared to PS. The effect of the weight ratio of montmorillonite on the thermal properties of the nanocomposites was also studied by TGA. Differential scanning calorimetry revealed that the addition of the nanoclay increased the glass-transition temperature. Moreover, degradation of the bromide chain-end functionality took place at low temperatures. Scanning electron microscopy showed that the average diameter of the fibers was around 500 nm. The dispersion of clay layers was also evaluated by Al atoms in the PS matrix with the energy-dispersive X-ray detection technique. Transmission electron microscopy confirmed the exfoliation of the nanoclay within the matrix. However, the clay layers were oriented along the nanofiber axis. (C) 2010 Wiley Periodicals, Inc. I Appl Polym Sci 120: 1431-1438, 2011