Trans-1,4-polyisoprene (TPI) nanofibers have been fabricated successfully through electrospinning technology. Through the control of electrospinning parameters, highly crystallized TPI fresh fibers composed mainly by beta phase were produced. Morphology and diameter of TPI nanofibers can be controlled by adjusting the electrospinning conditions. The in situ observations of FTIR spectra revealed that the crystallinity of the TPI fibers decreased with aging. While for TPI nanofibers aging at 45 A degrees C for 24 h, a decrease in crystallinity as well as beta to alpha transformation was observed with aging and these changings happened in the first 50 h during aging. The mechanism for beta-TPI formation during electrospinning process and the reduced crystallinity with aging were proposed.