Thermal properties such as melting temperature can well reflect the microstructure of the polymer material, and have practical implications in the application of nanofibers. In this work, we investigated the melting temperature of individual electrospun poly(vinylidene fluoride) (PVDF) nanofibers with diameters ranging from smaller than 200 nm to greater than 2 mu m by the local thermal analysis technique. The PVDF fibers obtained under four different conditions were found to crystallize into alpha and beta phases, and the fiber mats showed typical values in the crystallinity andT(m)with no significant difference among the four. However, analyses at single fiber level revealed broad distribution in diameter andT(m)for the fibers produced under identical electrospinning condition. TheT(m)of individual nanofibers was found to remain constant at large diameters and increase quickly when reducing the fiber diameter toward the nanoscale, andT(m)values of 220-230 degrees C were observed for the thinnest nanofibers, much higher than the typical values reported for bulk PVDF. TheT(m)and molecular orientation at different positions along a beaded fiber were analyzed, showing a similar distribution pattern with a minimum at the bead center and higher values when moving toward both directions. The results indicate that molecular orientation is the driving mechanism for the observed correlation between theT(m)and the diameter of the nanofibers.