Abstract: A novel approach for toughening the carbon fiber/epoxy composite using electrospun polysulfone (PSF) nanofibers was performed．As-received nanofibers with random orientation were directly electrospun onto the layers of carbon fiber/epoxy prepregs to toughen the composites．The ratio of different solvents and the concentration of PSF solutions， which affected the diameter and distribution of PSF nanofibers，were discussed．The mode Ⅱ interlaminar fracture toughness (G_ⅡC) of the nanofibers toughened composites was tested，compared to those of PSF films toughened composites. G_ⅡC increased 54%，130% and 177% by loading 1%，3% and 5% mass fraction of nanofibers，which was higher than those of the same content PSF films toughened composites．The SEM images show that PSF particles distributed through the whole composite interleaves and exhibited random alignment. The ILSS of nanofibers and PSF films toughened composites decreases，while the reductions of ILSS for PSF films toughened composites are larger．DMTA tests reveal good compatibility between nanofibers and epoxy matrix，compared to PSF film toughened composites.