Abstract: In this study, the nanoscale welding and morphology changes of multi-walled carbon nanotubes (MWCNTs) were focused experimentally. After 1064nm fiber laser irradiation, MWCNTs can be welded together, which was observed by scanning electron microscope (SEM). Effects of laser power density and irradiation time on the welding and morphology changes of MWCNTs were investigated. Experiments show that nanoscale welding is achieved at a total power density of 90W/cm ². Due to the thermal accumulation, holes and na-noparticles are induced during higher total power density irradiation and aspects ratios of MWCNTs are strongly reduced.