Electrospinning has been emerging as one of the most efficient methods to fabricate polymer nanofibers. In this paper, PS/clay nanocomposite fibers with varying diameters were electrospun onto solid substrates. The fiber diameters were adjusted from 4 mu m to 150 nm by changing the solution concentration. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used to characterize the fiber morphology. Shear modulation force microscopy (SMFM) was utilized to investigate the surface nanomechanical properties of electrospun fibers as a function of the fiber diameter and temperature. In the absence of clay, no change in T, was observed, even though a large increase of shear modulus below the glass transition temperature was found. This effect was postulated to result from the molecular chain alignment during electrospinning. The addition of functionalized clays to the spinning solution produced fibers with a highly aligned montmorillonite layer structure at a clay concentration of 4 wt %. Clay agglomerates were observed at higher concentrations. The existence of clay further enhanced the shear modulus of fibers and increased the glass transition temperature by nearly 20 degrees C.